Method for supporting mobility for terminal in wireless communication system and terminal utilizing the method

ABSTRACT

The present invention, a method for operating a reduced power mode carried out by a first terminal in a wireless communication system, comprises the steps of: determining whether a second terminal is to act as a proxy for a mobility-associated procedure of the first terminal; and, on the basis of the determination, entering a reduced power mode, wherein, in the reduced power mode, the mobility-associated procedure for the first terminal may be omitted or carried out with low frequency.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to wireless communications, and moreparticularly, relates to a method for supporting the mobility for aterminal in a wireless communication system and a terminal utilizing thesame.

Related Art

In the International Telecommunication Union Radio communication sector(ITU-R), the standardization task of the International MobileTelecommunication (IMT)-Advanced, which is the next generation mobilecommunication system after the third generation, has been progressed.The IMT-Advanced aims to support the multimedia service based inInternet Protocol (IP) with the data transmission rate of 1 Gbps in stopand low speed mobile state, and 100 Mbps in high speed mobile state.

3rd Generation Partnership Project (3GPP) is a system standard thatsatisfies the requirements of the IMT-Advanced, and is preparingLTE-Advanced (LTE-A) that improves Long Term Evolution (LTE) based onthe Orthogonal Frequency Division Multiple Access (OFDMA)/SingleCarrier-Frequency Division Multiple Access (SC-FDMA) transmissionscheme.

Recently, owing to the development of the information communicationindustry, a user may have a variety of terminals simultaneously. Forexample, the case is increasing that a user has a smart phone and asmart watch, a user has a smart phone and a tablet PC, or a user has asmart watch and a tablet PC.

In the case that all of the terminals possessed by a user perform theprocedure for each of the conventional cellular operations, an operationtime of a terminal of which battery capacity is relatively small isshorter than an operation time of a terminal of which battery capacityis relatively great. For example, in the case that a user has both of asmart phone and a smart watch, and both of the smart phone and the smartwatch perform the cellular operation, a battery of the smart watch ofwhich battery capacity is smaller than that of the smart phone isdischarged fast, and accordingly, the function of the smart watch is notfully fulfilled. Accordingly, a method and apparatus is required tosolve the problem described above.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a method for supportingthe mobility for a terminal in a wireless communication system and aterminal utilizing the same.

In an aspect, a method for operating a power saving mode performed by afirst user equipment (UE) in a wireless communication system isprovided. The method comprises determining whether a second UE acts aproxy for a procedure in relation to mobility for the first UE andentering a power saving mode based on the determination, wherein theprocedure in relation to mobility of the first UE is not performed orperformed with low frequency in the power saving mode.

A user of the first UE and a user of the second UE may be identical, andwherein an amount of battery of the first UE is smaller than an amountof battery of the second UE.

The method may further comprise transmitting information of thedetermination to a network.

In the power saving mode, a measurement of a serving cell and aneighboring cell required for performing the procedure in relation tomobility may be not performed, a measurement of a serving cell and aneighboring cell required for performing the procedure in relation tomobility is performed with low frequency in comparison with the secondUE, a paging reception is omitted, or a paging reception is performedwith low frequency.

The method may further comprise receiving information of a serving cellthrough the second UE, in the power saving mode.

The information of the serving cell may include at least one of aserving cell identity, a serving cell frequency, system information set1, or system information set 2.

The method may further comprise receiving a paging message for the firstUE through the second UE and returning to a normal mode based on theinformation of the serving cell.

The method may further comprise transmitting the information indicatingreturning to the normal mode to the second UE after returning to thenormal mode.

The method may further comprise returning to a normal mode based on theinformation of the serving cell when a mobile originating data isgenerated.

The method may further comprise receiving a paging message for the firstUE through the second UE, requesting the information of the serving cellto the second UE and returning to a normal mode based on the informationof the serving cell, wherein receiving the information of the servingcell through the second UE is performed after requesting the informationof the serving cell.

The method may further comprise requesting the information of theserving cell to the second UE when a mobile originating data isgenerated and returning to a normal mode based on the information of theserving cell, wherein receiving the information of the serving cellthrough the second UE is performed after requesting the information ofthe serving cell to the second UE.

The first UE may be in a Radio Resource Control (RRC) idle state.

In other aspects, a user equipment (UE) is provided. The UE comprises aradio frequency (RF) unit configured to transmit and receive a radiosignal and a processor configured to operate with being connected withthe RF unit, wherein the processor is configured to perform determiningwhether another UE acts a proxy for a procedure in relation to mobilityfor the UE and entering a power saving mode based on the determination,wherein the procedure in relation to mobility of the UE is not performedor performed with low frequency in the power saving mode.

According to the present invention, a method for supporting the mobilityfor a terminal in a wireless communication system and a terminalutilizing the same are provided.

According to the present invention, a terminal may receive theinformation of other terminal from a network in place of the otherterminal, and accordingly, may transmit the received information to theother UE.

According to the present invention, a terminal may receive theinformation of other terminal from a network in place of the otherterminal, and in this case, the other terminal may enter a state forsaving power while the terminal receives the information.

According to the present invention, a terminal may receive the mobilityrelated information for other terminal from a network, and in this case,the other terminal may enter a state for saving power while the terminalreceives the mobility related information. That is, while the terminalreceives the mobility related information for other terminal in place ofthe other terminal, the other terminal enters a state for saving power,and accordingly, the other terminal may save power and the batteryefficiency of the other terminal increases.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a wireless communication system to which the presentinvention is applied.

FIG. 2 is a diagram showing a wireless protocol architecture for a userplane.

FIG. 3 is a diagram showing a wireless protocol architecture for acontrol plane.

FIG. 4 is a flowchart illustrating the operation of UE in the RRC idlestate.

FIG. 5 is a flowchart illustrating a procedure of establishing RRCconnection.

FIG. 6 is a flowchart illustrating an RRC connection reconfigurationprocedure.

FIG. 7 is a diagram illustrating an RRC connection re-establishmentprocedure.

FIG. 8 illustrates sub states where the terminal may have in an RRC_IDLEstate and a sub state transition process.

FIG. 9 illustrates a reference structure for a ProSe.

FIG. 10 is a flowchart for a handover ready procedure.

FIG. 11 is a flowchart for a handover resource allocation procedure.

FIG. 12 is a flowchart schematically illustrating a procedure of paging.

FIG. 13 is a flowchart for a procedure of determining a proxy-operationperformance according to an embodiment of the present invention.

FIG. 14 is a flowchart for a procedure of determining a proxy-operationperformance according to another embodiment of the present invention.

FIG. 15 is a flowchart for a procedure of determining a proxy-operationperformance according to still another embodiment of the presentinvention.

FIG. 16 illustrates a communication method performed by the second UEaccording to an embodiment of the present invention.

FIG. 17 illustrates an example of transmitting data to the second UE bythe first UE.

FIG. 18 illustrates an example of a protocol data unit (PDU) formatavailable to be used in an inter-UE direct link.

FIG. 19 illustrates an operation method for a proxy transmission of thesecond UE.

FIG. 20 is a flowchart for a method for acting as a proxy for themobility operation according to an embodiment of the present invention.

FIG. 21 is a flowchart of a method for acting as a proxy for the pagingaccording to an embodiment of the present invention.

FIG. 22 is a flowchart for a method for acting as a proxy for themobility operation according to another embodiment of the presentinvention.

FIG. 23 is a flowchart for a method for acting as a proxy for themobility operation according to another embodiment of the presentinvention.

FIG. 24 is a block diagram illustrating a UE in which the embodiments ofthe present invention are implemented.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

FIG. 1 shows a wireless communication system to which the presentinvention is applied. The wireless communication system may also bereferred to as an evolved-UMTS terrestrial radio access network(E-UTRAN) or a long term evolution (LTE)/LTE-A system.

The E-UTRAN includes at least one base station (BS) 20 which provides acontrol plane and a user plane to a user equipment (UE) 10. The UE 10may be fixed or mobile, and may be referred to as another terminology,such as a mobile station (MS), a user terminal (UT), a subscriberstation (SS), a mobile terminal (MT), a wireless device, etc. The BS 20is generally a fixed station that communicates with the UE 10 and may bereferred to as another terminology, such as an evolved node-B (eNB), abase transceiver system (BTS), an access point, etc.

The BSs 20 are interconnected by means of an X2 interface. The BSs 20are also connected by means of an S1 interface to an evolved packet core(EPC) 30, more specifically, to a mobility management entity (MME)through S1-MME and to a serving gateway (S-GW) through S1-U.

The EPC 30 includes an MME, an S-GW, and a packet data network-gateway(P-GW). The MME has access information of the UE or capabilityinformation of the UE, and such information is generally used formobility management of the UE. The S-GW is a gateway having an E-UTRANas an end point. The P-GW is a gateway having a PDN as an end point.

Layers of a radio interface protocol between the UE and the network canbe classified into a first layer (L1), a second layer (L2), and a thirdlayer (L3) based on the lower three layers of the open systeminterconnection (OSI) model that is well-known in the communicationsystem. Among them, a physical (PHY) layer belonging to the first layerprovides an information transfer service by using a physical channel,and a radio resource control (RRC) layer belonging to the third layerserves to control a radio resource between the UE and the network. Forthis, the RRC layer exchanges an RRC message between the UE and the BS.

FIG. 2 is a diagram showing a wireless protocol architecture for a userplane. FIG. 3 is a diagram showing a wireless protocol architecture fora control plane. The user plane is a protocol stack for user datatransmission. The control plane is a protocol stack for control signaltransmission.

Referring to FIGS. 2 and 3, a PHY layer provides an upper layer with aninformation transfer service through a physical channel. The PHY layeris connected to a medium access control (MAC) layer which is an upperlayer of the PHY layer through a transport channel. Data is transferredbetween the MAC layer and the PHY layer through the transport channel.The transport channel is classified according to how and with whatcharacteristics data is transferred through a radio interface.

Data is moved between different PHY layers, that is, the PHY layers of atransmitter and a receiver, through a physical channel. The physicalchannel may be modulated according to an Orthogonal Frequency DivisionMultiplexing (OFDM) scheme, and use the time and frequency as radioresources.

The functions of the MAC layer include mapping between a logical channeland a transport channel and multiplexing and demultiplexing to atransport block that is provided through a physical channel on thetransport channel of a MAC Service Data Unit (SDU) that belongs to alogical channel. The MAC layer provides service to a Radio Link Control(RLC) layer through the logical channel.

The functions of the RLC layer include the concatenation, segmentation,and reassembly of an RLC SDU. In order to guarantee various types ofQuality of Service (QoS) required by a Radio Bearer (RB), the RLC layerprovides three types of operation mode: Transparent Mode (TM),Unacknowledged Mode (UM), and Acknowledged Mode (AM). AM RLC provideserror correction through an Automatic Repeat Request (ARQ).

The RRC layer is defined only on the control plane. The RRC layer isrelated to the configuration, reconfiguration, and release of radiobearers, and is responsible for control of logical channels, transportchannels, and PHY channels. An RB means a logical route that is providedby the first layer (PHY layer) and the second layers (MAC layer, the RLClayer, and the PDCP layer) in order to transfer data between UE and anetwork.

The function of a Packet Data Convergence Protocol (PDCP) layer on theuser plane includes the transfer of user data and header compression andciphering. The function of the PDCP layer on the user plane furtherincludes the transfer and encryption/integrity protection of controlplane data.

What an RB is configured means a procedure of defining thecharacteristics of a wireless protocol layer and channels in order toprovide specific service and configuring each detailed parameter andoperating method. An RB can be divided into two types of a Signaling RB(SRB) and a Data RB (DRB). The SRB is used as a passage through which anRRC message is transmitted on the control plane, and the DRB is used asa passage through which user data is transmitted on the user plane.

If RRC connection is established between the RRC layer of UE and the RRClayer of an E-UTRAN, the UE is in the RRC connected state. If not, theUE is in the RRC idle state.

A downlink transport channel through which data is transmitted from anetwork to UE includes a broadcast channel (BCH) through which systeminformation is transmitted and a downlink shared channel (SCH) throughwhich user traffic or control messages are transmitted. Traffic or acontrol message for downlink multicast or broadcast service may betransmitted through the downlink SCH, or may be transmitted through anadditional downlink multicast channel (MCH). Meanwhile, an uplinktransport channel through which data is transmitted from UE to a networkincludes a random access channel (RACH) through which an initial controlmessage is transmitted and an uplink shared channel (SCH) through whichuser traffic or control messages are transmitted.

Logical channels that are placed over the transport channel and that aremapped to the transport channel include a broadcast control channel(BCCH), a paging control channel (PCCH), a common control channel(CCCH), a multicast control channel (MCCH), and a multicast trafficchannel (MTCH).

The physical channel includes several OFDM symbols in the time domainand several subcarriers in the frequency domain. One subframe includes aplurality of OFDM symbols in the time domain. An RB is a resourcesallocation unit, and includes a plurality of OFDM symbols and aplurality of subcarriers. Furthermore, each subframe may use specificsubcarriers of specific OFDM symbols (e.g., the first OFDM symbol) ofthe corresponding subframe for a physical downlink control channel(PDCCH), that is, an L1/L2 control channel. A Transmission Time Interval(TTI) is a unit time for subframe transmission.

The RRC state of UE and an RRC connection method are described below.

The RRC state means whether or not the RRC layer of UE is logicallyconnected to the RRC layer of the E-UTRAN. A case where the RRC layer ofUE is logically connected to the RRC layer of the E-UTRAN is referred toas an RRC connected state. A case where the RRC layer of UE is notlogically connected to the RRC layer of the E-UTRAN is referred to as anRRC idle state. The E-UTRAN may check the existence of corresponding UEin the RRC connected state in each cell because the UE has RRCconnection, so the UE may be effectively controlled. In contrast, theE-UTRAN is unable to check UE in the RRC idle state, and a Core Network(CN) manages UE in the RRC idle state in each tracking area, that is,the unit of an area greater than a cell. That is, the existence ornon-existence of UE in the RRC idle state is checked only for each largearea. Accordingly, the UE needs to shift to the RRC connected state inorder to be provided with common mobile communication service, such asvoice or data.

When a user first powers UE, the UE first searches for a proper cell andremains in the RRC idle state in the corresponding cell. The UE in theRRC idle state establishes RRC connection with an E-UTRAN through an RRCconnection procedure when it is necessary to set up the RRC connection,and shifts to the RRC connected state. A case where UE in the RRC idlestate needs to set up RRC connection includes several cases. Forexample, the cases may include a need to send uplink data for a reason,such as a call attempt by a user, and to send a response message as aresponse to a paging message received from an E-UTRAN.

A Non-Access Stratum (NAS) layer placed over the RRC layer performsfunctions, such as session management and mobility management.

In the NAS layer, in order to manage the mobility of UE, two types ofstates: EPS Mobility Management-REGISTERED (EMM-REGISTERED) andEMM-DEREGISTERED are defined. The two states are applied to UE and theMME. UE is initially in the EMM-DEREGISTERED state. In order to access anetwork, the UE performs a procedure of registering it with thecorresponding network through an initial attach procedure. If the attachprocedure is successfully performed, the UE and the MME become theEMM-REGISTERED state.

In order to manage signaling connection between UE and the EPC, twotypes of states: an EPS Connection Management (ECM)-IDLE state and anECM-CONNECTED state are defined. The two states are applied to UE andthe MME. When the UE in the ECM-IDLE state establishes RRC connectionwith the E-UTRAN, the UE becomes the ECM-CONNECTED state. The MME in theECM-IDLE state becomes the ECM-CONNECTED state when it establishes S1connection with the E-UTRAN. When the UE is in the ECM-IDLE state, theE-UTRAN does not have information about the context of the UE.Accordingly, the UE in the ECM-IDLE state performs procedures related toUE-based mobility, such as cell selection or cell reselection, without aneed to receive a command from a network. In contrast, when the UE is inthe ECM-CONNECTED state, the mobility of the UE is managed in responseto a command from a network. If the location of the UE in the ECM-IDLEstate is different from a location known to the network, the UE informsthe network of its corresponding location through a tracking area updateprocedure.

System information is described below.

System information includes essential information that needs to be knownby UE in order for the UE to access a BS. Accordingly, the UE needs tohave received all pieces of system information before accessing the BS,and needs to always have the up-to-date system information. Furthermore,the BS periodically transmits the system information because the systeminformation is information that needs to be known by all UEs within onecell. The system information is divided into a Master Information Block(MIB) and a plurality of System Information Blocks (SIBs).

The MIB may include a limited number of parameters that are mostessential and most frequently transmitted when other information isrequired to be obtained from a cell. UE first searches for an MIB afterdownlink synchronization. The MIB may include information, such as anSFN that supports downlink channel bandwidth, a PHICH configuration, andsynchronization and operates as a timing criterion and an eNB transmitantenna configuration. The MIB may be transmitted on a broadcast channel(BCH) through broadcasting.

SystemInformationBlockType1 (SIB1) of included SIBs is included in a“SystemInformationBlockType1” message and transmitted. The remainingSIBs other than the SIB1 is included in a system information message andtransmitted. To map the SIBs to the system information message may beflexibly configured by a scheduling information list parameter includedin the SIB1. In this case, each of the SIBs is included in a singlesystem information message, and only SIBs having the same schedulingrequirement value (e.g. cycle) may be mapped to the same systeminformation message. Furthermore, a SystemInformationBlockType2 (SIB2)is always mapped to a system information message corresponding to thefirst entry within the system information message list of a schedulinginformation list. A plurality of system information messages may betransmitted within the same cycle. The SIB1 and all the systeminformation messages are transmitted on a DL-SCH.

In addition to broadcast transmission, in an E-UTRAN, the SIB1 may bededicated-signaled in the state in which it includes a parameterconfigured like an existing configured value. In this case, the SIB1 maybe included in an RRC connection reconfiguration message andtransmitted.

The SIB1 includes information related to UE cell access, and defines thescheduling of other SIBs. The SIB1 may include information related tothe PLMN identifiers of a network, tracking area code (TAC) and a cellID, a cell barring status indicative of whether a cell is a cell onwhich camp-on is possible, the lowest reception level required within acell which is used as cell reselection criterion, and the transmissiontime and cycle of other SIBs.

The SIB2 may include radio resource configuration information common toall pieces of UE. The SIB2 may include information related to an uplinkcarrier frequency and uplink channel bandwidth, an RACH configuration, apage configuration, an uplink power control configuration, a soundingreference signal configuration, a PUCCH configuration supportingACK/NACK transmission, and a PUSCH configuration.

UE may apply a procedure for obtaining system information and detectinga change of system information to a primary cell (PCell) only. In asecondary cell (SCell), when a corresponding SCell is added, an E-UTRANmay provide all of pieces of system information related to an RRCconnection state operation through dedicated signaling. When systeminformation related to a configured SCell is changed, an E-UTRAN mayrelease an SCell that is taken into consideration and subsequently addthe changed system information. This may be performed along with asingle RRC connection reconfiguration message. An E-UTRAN may configureparameter values different from a value broadcasted within an SCell thathas been taken into consideration through dedicated signaling.

UE needs to guarantee the validity of a specific type of systeminformation, and such system information is called required systeminformation. The required system information may be defined as follows.

-   -   If UE is an RRC idle state: The UE needs to be guaranteed so        that it has the valid versions of the MIB and the SIB1 in        addition to the SIB2 to SIB8. This may comply with the support        of a radio access technology (RAT) that is taken into        consideration.    -   If UE is an RRC connection state: The UE needs to be guaranteed        so that it has the valid versions of the MIB, the SIB1, and the        SIB2.

In general, the validity of system information may be guaranteed up to amaximum of 3 hours after the system information is obtained.

In general, service that is provided to UE by a network may beclassified into three types as follows. Furthermore, the UE differentlyrecognizes the type of cell depending on what service may be provided tothe UE. In the following description, a service type is first described,and the type of cell is described.

1) Limited service: this service provides emergency calls and anEarthquake and Tsunami Warning System (ETWS), and may be provided by anacceptable cell.

2) Suitable service: this service means public service for common uses,and may be provided by a suitable cell (or a normal cell).

3) Operator service: this service means service for communicationnetwork operators. This cell may be used by only communication networkoperators, but may not be used by common users.

In relation to a service type provided by a cell, the type of cell maybe classified as follows.

1) An acceptable cell: this cell is a cell from which UE may be providedwith limited service. This cell is a cell that has not been barred froma viewpoint of corresponding UE and that satisfies the cell selectioncriterion of the UE.

2) A suitable cell: this cell is a cell from which UE may be providedwith suitable service. This cell satisfies the conditions of anacceptable cell and also satisfies additional conditions. The additionalconditions include that the suitable cell needs to belong to a PublicLand Mobile Network (PLMN) to which corresponding UE may access and thatthe suitable cell is a cell on which the execution of a tracking areaupdate procedure by the UE is not barred. If a corresponding cell is aCSG cell, the cell needs to be a cell to which UE may access as a memberof the CSG.

3) A barred cell: this cell is a cell that broadcasts informationindicative of a barred cell through system information.

4) A reserved cell: this cell is a cell that broadcasts informationindicative of a reserved cell through system information.

FIG. 4 is a flowchart illustrating the operation of UE in the RRC idlestate. FIG. 4 illustrates a procedure in which UE that is initiallypowered on experiences a cell selection procedure, registers it with anetwork, and then performs cell reselection if necessary.

Referring to FIG. 4, the UE selects Radio Access Technology (RAT) inwhich the UE communicates with a Public Land Mobile Network (PLMN), thatis, a network from which the UE is provided with service (S410).Information about the PLMN and the RAT may be selected by the user ofthe UE, and the information stored in a Universal Subscriber IdentityModule (USIM) may be used.

The UE selects a cell that has the greatest value and that belongs tocells having measured BS and signal intensity or quality greater than aspecific value (cell selection) (S420). In this case, the UE that ispowered off performs cell selection, which may be called initial cellselection. A cell selection procedure is described later in detail.After the cell selection, the UE receives system informationperiodically by the BS. The specific value refers to a value that isdefined in a system in order for the quality of a physical signal indata transmission/reception to be guaranteed. Accordingly, the specificvalue may differ depending on applied RAT.

If network registration is necessary, the UE performs a networkregistration procedure (S430). The UE registers its information (e.g.,an IMSI) with the network in order to receive service (e.g., paging)from the network. The UE does not register it with a network whenever itselects a cell, but registers it with a network when information aboutthe network (e.g., a Tracking Area Identity (TAI)) included in systeminformation is different from information about the network that isknown to the UE.

The UE performs cell reselection based on a service environment providedby the cell or the environment of the UE (S440). If the value of theintensity or quality of a signal measured based on a BS from which theUE is provided with service is lower than that measured based on a BS ofa neighboring cell, the UE selects a cell that belongs to other cellsand that provides better signal characteristics than the cell of the BSthat is accessed by the UE. This procedure is called cell reselectiondifferently from the initial cell selection of the No. 2 procedure. Inthis case, temporal restriction conditions are placed in order for acell to be frequently reselected in response to a change of signalcharacteristic. A cell reselection procedure is described later indetail.

FIG. 5 is a flowchart illustrating a procedure of establishing RRCconnection.

UE sends an RRC connection request message that requests RRC connectionto a network (S510). The network sends an RRC connection establishmentmessage as a response to the RRC connection request (S520). Afterreceiving the RRC connection establishment message, the UE enters RRCconnected mode.

The UE sends an RRC connection establishment complete message used tocheck the successful completion of the RRC connection to the network(S530).

FIG. 6 is a flowchart illustrating an RRC connection reconfigurationprocedure. An RRC connection reconfiguration is used to modify RRCconnection. This is used to establish/modify/release RBs, performhandover, and set up/modify/release measurements.

A network sends an RRC connection reconfiguration message for modifyingRRC connection to UE (S610). As a response to the RRC connectionreconfiguration message, the UE sends an RRC connection reconfigurationcomplete message used to check the successful completion of the RRCconnection reconfiguration to the network (S620).

Hereinafter, a public land mobile network (PLMN) is described.

The PLMN is a network which is disposed and operated by a mobile networkoperator. Each mobile network operator operates one or more PLMNs. EachPLMN may be identified by a Mobile Country Code (MCC) and a MobileNetwork Code (MNC). PLMN information of a cell is included in systeminformation and broadcasted.

In PLMN selection, cell selection, and cell reselection, various typesof PLMNs may be considered by the terminal.

Home PLMN (HPLMN): PLMN having MCC and MNC matching with MCC and MNC ofa terminal IMSI.

Equivalent HPLMN (EHPLMN): PLMN serving as an equivalent of an HPLMN.

Registered PLMN (RPLMN): PLMN successfully finishing locationregistration.

Equivalent PLMN (EPLMN): PLMN serving as an equivalent of an RPLMN.

Each mobile service consumer subscribes in the HPLMN. When a generalservice is provided to the terminal through the HPLMN or the EHPLMN, theterminal is not in a roaming state. Meanwhile, when the service isprovided to the terminal through a PLMN except for the HPLMN/EHPLMN, theterminal is in the roaming state. In this case, the PLMN refers to aVisited PLMN (VPLMN).

When UE is initially powered on, the UE searches for available PublicLand Mobile Networks (PLMNs) and selects a proper PLMN from which the UEis able to be provided with service. The PLMN is a network that isdeployed or operated by a mobile network operator. Each mobile networkoperator operates one or more PLMNs. Each PLMN may be identified byMobile Country Code (MCC) and Mobile Network Code (MNC). Informationabout the PLMN of a cell is included in system information andbroadcasted. The UE attempts to register it with the selected PLMN. Ifregistration is successful, the selected PLMN becomes a Registered PLMN(RPLMN). The network may signalize a PLMN list to the UE. In this case,PLMNs included in the PLMN list may be considered to be PLMNs, such asRPLMNs. The UE registered with the network needs to be able to be alwaysreachable by the network. If the UE is in the ECM-CONNECTED state(identically the RRC connection state), the network recognizes that theUE is being provided with service. If the UE is in the ECM-IDLE state(identically the RRC idle state), however, the situation of the UE isnot valid in an eNB, but is stored in the MME. In such a case, only theMME is informed of the location of the UE in the ECM-IDLE state throughthe granularity of the list of Tracking Areas (TAs). A single TA isidentified by a Tracking Area Identity (TAI) formed of the identifier ofa PLMN to which the TA belongs and Tracking Area Code (TAC) thatuniquely expresses the TA within the PLMN.

Thereafter, the UE selects a cell that belongs to cells provided by theselected PLMN and that has signal quality and characteristics on whichthe UE is able to be provided with proper service.

The following is a detailed description of a procedure of selecting acell by a terminal.

When power is turned-on or the terminal is located in a cell, theterminal performs procedures for receiving a service byselecting/reselecting a suitable quality cell.

A terminal in an RRC idle state should prepare to receive a servicethrough the cell by always selecting a suitable quality cell. Forexample, a terminal where power is turned-on just before should selectthe suitable quality cell to be registered in a network. If the terminalin an RRC connection state enters in an RRC idle state, the terminalshould selects a cell for stay in the RRC idle state. In this way, aprocedure of selecting a cell satisfying a certain condition by theterminal in order to be in a service idle state such as the RRC idlestate refers to cell selection. Since the cell selection is performed ina state that a cell in the RRC idle state is not currently determined,it is important to select the cell as rapid as possible. Accordingly, ifthe cell provides a wireless signal quality of a predetermined level orgreater, although the cell does not provide the best wireless signalquality, the cell may be selected during a cell selection procedure ofthe terminal.

A method and a procedure of selecting a cell by a terminal in a 3GPP LTEis described with reference to 3GPP TS 36.304 V8.5.0 (2009-03) “UserEquipment (UE) procedures in idle mode (Release 8)”.

A cell selection procedure is basically divided into two types.

The first is an initial cell selection procedure. In this procedure, UEdoes not have preliminary information about a wireless channel.Accordingly, the UE searches for all wireless channels in order to findout a proper cell. The UE searches for the strongest cell in eachchannel. Thereafter, if the UE has only to search for a suitable cellthat satisfies a cell selection criterion, the UE selects thecorresponding cell.

Next, the UE may select the cell using stored information or usinginformation broadcasted by the cell. Accordingly, cell selection may befast compared to an initial cell selection procedure. If the UE has onlyto search for a cell that satisfies the cell selection criterion, the UEselects the corresponding cell. If a suitable cell that satisfies thecell selection criterion is not retrieved though such a procedure, theUE performs an initial cell selection procedure.

A cell selection criterion may be defined as in Equation 1 below.Following Equation 1 can be referred to as measurement for determiningwhether or not S-criterion is satisfied.

Srxlev>0AND Squal>0,  [Equation 1]

-   -   where:    -   Srxlev=Q_(rxlevmeas)−(Q_(rxlevmin)+Q_(rxlevminoffset))−P_(compensation),    -   Squa1=Q_(qualmeas)−(Q_(qualmin)+Q_(qualminoffset))

In this case, in Equation 1, the variables may be defined as in Table 1below.

TABLE 1 Srxlev Cell selection RX level value (dB) Squal Cell selectionquality value (dB) Q_(rxlevmeas) Measured cell RX level value (RSRP)Q_(qualmeas) Measured cell quality value (RSRQ) Q_(rxlevmin) Minimumrequired RX level in the cell (dBm) Q_(qualmin) Minimum required qualitylevel in the cell (dB) Q_(rxlminoffset) Offset to the signalledQ_(rxlevmin) taken into account in the Srxlev evaluation as a result ofa periodic search for a higher priority PLMN while camped normally in aVPLMN Q_(qualminoffset) Offset to the signalled Q_(qualmin) taken intoaccount in the Squal evaluation as a result of a periodic search for ahigher priority PLMN while camped normally in a VPLMN Pcompensationmax(P_(EMAX) − P_(PowerClass), 0) (dB) P_(EMAX) Maximum TX power levelan UE may use when transmitting on the uplink in the cell (dBm) definedas P_(EMAX) in [TS 36.101] P_(PowerClass) Maximum RF output power of theUE (dBm) according to the UE power class as defined in [TS 36.101]

Q_(rxlevminoffset) and Q_(qualminoffset), that is, signaled values, arethe results of periodic discovery for a PLMN having higher prioritywhile UE camps on a normal cell within a VPLMN, and may be applied onlywhen cell selection is evaluated. As described above, during theperiodic discovery of a PLMN having higher priority, UE may perform cellselection evaluation using parameter values stored from another cell ofthe PLMN having such higher priority.

After UE selects any cell through a cell selection procedure, theintensity or quality of a signal between the UE and a BS may be changeddue to the mobility of the UE or a change of a radio environment.Accordingly, if the quality of the selected cell is changed, the UE mayselect another cell providing better quality.

After the UE selects a specific cell through the cell selectionprocedure, the intensity or quality of a signal between the UE and a BSmay be changed due to a change in the mobility or wireless environmentof the UE. Accordingly, if the quality of the selected cell isdeteriorated, the UE may select another cell that provides betterquality. If a cell is reselected as described above, the UE selects acell that provides better signal quality than the currently selectedcell. Such a procedure is called cell reselection. In general, a basicobject of the cell reselection procedure is to select a cell thatprovides UE with the best quality from a viewpoint of the quality of aradio signal.

In addition to the viewpoint of the quality of a radio signal, a networkmay determine priority corresponding to each frequency, and may informthe UE of the determined priorities. The UE that has received thepriorities preferentially takes into consideration the priorities in acell reselection procedure compared to a radio signal quality criterion.

As described above, there is a method of selecting or reselecting a cellaccording to the signal characteristics of a wireless environment. Inselecting a cell for reselection when a cell is reselected, thefollowing cell reselection methods may be present according to the RATand frequency characteristics of the cell.

-   -   Intra-frequency cell reselection: UE reselects a cell having the        same center frequency as that of RAT, such as a cell on which        the UE camps on.    -   Inter-frequency cell reselection: UE reselects a cell having a        different center frequency from that of RAT, such as a cell on        which the UE camps on    -   Inter-RAT cell reselection: UE reselects a cell that uses RAT        different from RAT on which the UE camps

The principle of a cell reselection procedure is as follows.

First, UE measures the quality of a serving cell and neighbor cells forcell reselection.

Second, cell reselection is performed based on a cell reselectioncriterion. The cell reselection criterion has the followingcharacteristics in relation to the measurements of a serving cell andneighbor cells.

Intra-frequency cell reselection is basically based on ranking. Rankingis a task for defining a criterion value for evaluating cell reselectionand numbering cells using criterion values according to the size of thecriterion values. A cell having the best criterion is commonly calledthe best-ranked cell. The cell criterion value is based on the value ofa corresponding cell measured by UE, and may be a value to which afrequency offset or cell offset has been applied, if necessary.

Inter-frequency cell reselection is based on frequency priority providedby a network. UE attempts to camp on a frequency having the highestfrequency priority. A network may provide frequency priority that willbe applied by UEs within a cell in common through broadcastingsignaling, or may provide frequency-specific priority to each UE throughUE-dedicated signaling. A cell reselection priority provided throughbroadcast signaling may refer to a common priority. A cell reselectionpriority for each terminal set by a network may refer to a dedicatedpriority. If receiving the dedicated priority, the terminal may receivea valid time associated with the dedicated priority together. Ifreceiving the dedicated priority, the terminal starts a validity timerset as the received valid time together therewith. While the valid timeris operated, the terminal applies the dedicated priority in the RRC idlemode. If the valid timer is expired, the terminal discards the dedicatedpriority and again applies the common priority.

For the inter-frequency cell reselection, a network may provide UE witha parameter (e.g., a frequency-specific offset) used in cell reselectionfor each frequency. For the intra-frequency cell reselection or theinter-frequency cell reselection, a network may provide UE with aNeighboring Cell List (NCL) used in cell reselection. The NCL includes acell-specific parameter (e.g., a cell-specific offset) used in cellreselection. For the intra-frequency or inter-frequency cellreselection, a network may provide UE with a cell reselection black listused in cell reselection.

The UE does not perform cell reselection on a cell included in the blacklist.

Ranking performed in a cell reselection evaluation procedure isdescribed below.

A ranking criterion used to give the priority of a cell is defined as inEquation 2.

R _(s) =Q _(meas,s) +Q _(hyst) ,R _(n) =Q _(meas,n) −Q_(offset)  [Equation 2]

In Equation 2, Rs is the ranking criterion of a serving cell on which UEnow camps, Rn is the ranking criterion of a neighboring cell, Qmeas,s isthe quality value of the serving cell measured by the UE, Qmeas,n is thequality value of the neighboring cell measured by the UE, Qhyst is ahysteresis value for ranking, and Qoffset is an offset between the twocells.

In Intra-frequency, if UE receives an offset “Qoffsets,n” between aserving cell and a neighbor cell, Qoffset=Qoffsets,n. If UE does notQoffsets,n, Qoffset=0.

In Inter-frequency, if UE receives an offset “Qoffsets,n” for acorresponding cell, Qoffset=Qoffsets,n+Qfrequency. If UE does notreceive “Qoffsets,n”, Qoffset=Qfrequency.

If the ranking criterion Rs of a serving cell and the ranking criterionRn of a neighbor cell are changed in a similar state, ranking priorityis frequency changed as a result of the change, and UE may alternatelyreselect the twos. Qhyst is a parameter that gives hysteresis to cellreselection so that UE is prevented from to alternately reselecting twocells.

UE measures RS of a serving cell and Rn of a neighbor cell according tothe above equation, considers a cell having the greatest rankingcriterion value to be the best-ranked cell, and reselects the cell.

In accordance with the criterion, it may be checked that the quality ofa cell is the most important criterion in cell reselection. If areselected cell is not a suitable cell, UE excludes a correspondingfrequency or a corresponding cell from the subject of cell reselection.

Hereinafter, radio link failure (RLF) will be described.

UE continues to perform measurements in order to maintain the quality ofa radio link with a serving cell from which the UE receives service. TheUE determines whether or not communication is impossible in a currentsituation due to the deterioration of the quality of the radio link withthe serving cell. If communication is almost impossible because thequality of the serving cell is too low, the UE determines the currentsituation to be an RLF.

If the RLF is determined, the UE abandons maintaining communication withthe current serving cell, selects a new cell through cell selection (orcell reselection) procedure, and attempts RRC connectionre-establishment with the new cell.

In the specification of 3GPP LTE, the following examples are taken ascases where normal communication is impossible.

-   -   A case where UE determines that there is a serious problem in        the quality of a downlink communication link (a case where the        quality of a PCell is determined to be low while performing RLM)        based on the radio quality measured results of the PHY layer of        the UE    -   A case where uplink transmission is problematic because a random        access procedure continues to fail in the MAC sublayer.    -   A case where uplink transmission is problematic because uplink        data transmission continues to fail in the RLC sublayer.    -   A case where handover is determined to have failed.    -   A case where a message received by UE does not pass through an        integrity check.

An RRC connection re-establishment procedure is described in more detailbelow.

FIG. 7 is a diagram illustrating an RRC connection re-establishmentprocedure.

Referring to FIG. 7, UE stops using all the radio bearers that have beenconfigured other than a Signaling Radio Bearer (SRB) #0, and initializesa variety of kinds of sublayers of an Access Stratum (AS) (S710).Furthermore, the UE configures each sublayer and the KW layer as adefault configuration. In this procedure, the UE maintains the RRCconnection state.

The UE performs a cell selection procedure for performing an RRCconnection reconfiguration procedure (S720). The cell selectionprocedure of the RRC connection re-establishment procedure may beperformed in the same manner as the cell selection procedure that isperformed by the UE in the RRC idle state, although the UE maintains theRRC connection state.

After performing the cell selection procedure, the UE determines whetheror not a corresponding cell is a suitable cell by checking the systeminformation of the corresponding cell (S730). If the selected cell isdetermined to be a suitable E-UTRAN cell, the UE sends an RRC connectionre-establishment request message to the corresponding cell (S740).

Meanwhile, if the selected cell is determined to be a cell that uses RATdifferent from that of the E-UTRAN through the cell selection procedurefor performing the RRC connection re-establishment procedure, the UEstops the RRC connection re-establishment procedure and enters the RRCidle state (S750).

The UE may be implemented to finish checking whether the selected cellis a suitable cell through the cell selection procedure and thereception of the system information of the selected cell. To this end,the UE may drive a timer when the RRC connection re-establishmentprocedure is started. The timer may be stopped if it is determined thatthe UE has selected a suitable cell. If the timer expires, the UE mayconsider that the RRC connection re-establishment procedure has failed,and may enter the RRC idle state. Such a timer is hereinafter called anRLF timer. In LTE spec TS 36.331, a timer named “T311” may be used as anRLF timer. The UE may obtain the set value of the timer from the systeminformation of the serving cell.

If an RRC connection re-establishment request message is received fromthe UE and the request is accepted, a cell sends an RRC connectionre-establishment message to the UE.

The UE that has received the RRC connection re-establishment messagefrom the cell reconfigures a PDCP sublayer and an RLC sublayer with anSRB1. Furthermore, the UE calculates various key values related tosecurity setting, and reconfigures a PDCP sublayer responsible forsecurity as the newly calculated security key values. Accordingly, theSRB 1 between the UE and the cell is open, and the UE and the cell mayexchange RRC control messages. The UE completes the restart of the SRB1,and sends an RRC connection re-establishment complete message indicativeof that the RRC connection re-establishment procedure has been completedto the cell (S760).

In contrast, if the RRC connection re-establishment request message isreceived from the UE and the request is not accepted, the cell sends anRRC connection re-establishment reject message to the UE.

If the RRC connection re-establishment procedure is successfullyperformed, the cell and the UE perform an RRC connection reconfigurationprocedure. Accordingly, the UE recovers the state prior to the executionof the RRC connection re-establishment procedure, and the continuity ofservice is guaranteed to the upmost.

FIG. 8 illustrates sub states where the terminal may have in an RRC_IDLEstate and a sub state transition process.

Referring to FIG. 8, a terminal performs an initial cell selectionprocess (S801). The initial cell selection process may be performed whenthere is no stored cell information with respect to the PLMN or asuitable cell is not found.

If the suitable cell is not found in the initial cell selection process,the terminal transitions to an any cell selection state (S802). Theoptional cell selection state represents a state which does not camp onin both of a suitable cell and an acceptable cell. The optional cellselection state is a state attempted by the terminal in order to find anacceptable cell of an optional PLMN which may camp on. When the terminalfinds no cells which may camp on, the terminal is continuouslymaintained in an optional cell selection state until the acceptable cellis found.

If the suitable cell is found in the initial cell selection process, thestate transits to a normal camp state (S803). The normal camp staterepresents a state which camps on the normal cell. A paging channel isselected according to information given through system information tomotor, and an evaluation process for cell reselection may be performed.

In the normal camp state (S803), if a cell reselection evaluationprocess (S804) is caused, the cell reselection evaluation process (S804)is performed. If a suitable cell is found in the cell reselectionevaluation process (S804), the terminal again transits to the normalcamp state (S803).

If an acceptable cell is found in the any cell selection state (S802),the terminal transits to an any cell camped state (S805). The any cellcamped state (S805) represents a state of camping on an acceptable cell.

In the any cell camped state (S805), the terminal may select a pagingchannel according to information given through system information tomonitor, and may perform a cell reselection evaluation process (S806).If the acceptable cell is not found in the cell reselection evaluationprocess (S806), the terminal transits the any cell selection state(S802).

Hereinafter, a D2D operation will be described. In the 3GPP LTE-A, aservice related to the D2D operation refers to Proximity based Services(ProSe). Hereinafter, the ProSe is an equivalent concept with the D2Doperation and the ProSe may be compatibly used with the D2D operation.The ProSe is now described.

The ProSe includes ProSe direct communication and ProSe directdiscovery. The ProSe direct communication presents communicationperformed by two or more adjacent terminals. The terminals may performcommunication using a protocol of a user plane. A ProSe-enabled UE meansa UE for supporting a process related to requirements of the ProSe.Unless otherwise defined, the ProSe-enabled UE includes both of a publicsafety UE and a non-public safety UE. The public safety UE represents aUE for supporting both of a public safety specified function and theProSe process. The non-public safety UE is a terminal which supports theProSe process but does not support the public safety specified function.

The ProSe direct discovery is a process where the ProSe-enabled UEdiscovers another ProSe-enabled UE. In this case, only ability of thetwo ProSe-enabled UEs is used. An EPC-level ProSe discovery signifies aprocess where an EPC determines whether 2 ProSe enable terminals areclosed to each other, and reports the close state thereof the two ProSeenabled terminals.

Hereinafter, the ProSe direct communication may refer to D2Dcommunication, and the ProSe direct discovery may refer to D2Ddiscovery.

FIG. 9 illustrates a reference structure for a ProSe.

Referring to FIG. 9, the reference structure for a ProSe includes aplurality of terminals having E-UTRAN, EPC, and ProSe applicationprogram, a ProSe application (APP) server, and a ProSe function.

An EPC is a representative example of the E-UTRAN. The EPC may includean MME, an S-GW, a P-GW, a policy and charging rules function (PCRF),and a home subscriber server (HSS).

The ProSe application server is a user of ProSe in order to make anapplication function. The ProSe application server may communicate withan application program in the terminal. The application program in theterminal may use a ProSe ability to make an application function.

The ProSe function may include at least one of following functions butis not limited thereto.

-   -   Interworking via a reference point towards the 3rd party        applications    -   Authorization and configuration of the UE for discovery and        direct communication)    -   Enable the function of the EPC level ProSe discovery    -   ProSe related new subscriber data and handling of data storage,        and also handling of ProSe identities    -   Security related function    -   Provide control towards the EPC for policy related function    -   Provide function for charging (via or outside of EPC, e.g.,        offline charging))

Hereinafter, a reference point and a reference interface will bedescribed in a reference structure for the ProSe.

-   -   PC1: a reference point between a ProSe application program in        the terminal and a ProSe application program in a ProSe        application server. The PC1 is used to define signaling        requirements in an application level.    -   PC2: is a reference point between the ProSe application server        and a ProSe function. The PC2 is used to define an interaction        between the ProSe application server and a ProSe function. An        application data update of a ProSe database of the ProSe        function may be an example of the interaction.    -   PC3: is a reference point between the terminal and the ProSe        function. The PC3 is used to define an interaction between the        terminal and the ProSe function. Configuration for ProSe        discovery and communication may be an example of the        interaction.    -   PC4: is a reference point between an EPC and the ProSe function.        The PC4 is used to define an interaction between the EPC and the        ProSe function. The interaction lay illustrate when a path for        1:1 communication or a ProSe service for real time session        management or mobility management are authorized.    -   PC5: is a reference point to use control/user plane for        discovery, communication, and relay between terminals, and 1:1        communication.    -   PC6: is a reference point to use a function such as ProSe        discovery between users included in different PLMNs.    -   SGi: may be used for application data and application level        control information exchange.

Hereinafter, the handover will be described.

A handover signaling procedure supports both of an inter-eNB handoverand an inter-RAT handover. In this case, the inter-RAT handover isinitiated through the S1 interface described above, and the inter-eNBhandover is initiated through X2 interface, generally.

However,

-   -   in the case that a source eNB is not an RN, and X2 is not        existed between a source eNB and a target eNB, or    -   in the case that a source eNB is an RN, and X2 is not existed        between a DeNB and a target eNB or X2 is not existed between a        source RN and a DeNB, or    -   in the case that a source eNB is an RN, and a serving MME of a        UE is not included in MME pool(s) connected with a target eNB,        or    -   in the case that it is configured to initiate a handover to a        specific eNB through S1 such that a source eNB is able to change        an EPC node (MME and/or serving GW), or    -   in the case that a source eNB is going to start an inter-eNB        handover through X2 but receives a negative response from a        target eNB with a specific cause value,

The inter-eNB handover is initiated through the S1 interface.

FIG. 10 is a flowchart for a handover ready procedure.

Referring to FIG. 10, a source eNB transmits a handover request messageto an MME (step, S1010).

Later, the source eNB receives a handover command message from the MME(step, S1020).

The source eNB may transmit the handover command message to a UE (step,S1030).

Upon receiving the handover command message from the source eNB (in thiscase, the handover command message includes information in relation to aradio interface (e.g., a handover command for the UE) a successfullyestablished Enhanced Radio Access Bearer (E-RAB) and an E-RAB of whichsetup is failed), the handover ready procedure is finished.

In the case that a handover resource allocation is failed (e.g., in thecase that there is no available resource on a target), the source eNBreceives a handover ready failure message, instead of receiving thehandover command message from the MME (step, S1040).

FIG. 11 is a flowchart for a handover resource allocation procedure.

Referring to FIG. 11, a target eNB receives a handover request messagefrom an MME (step, S1110), and the handover request message may includean E-RAB which is required to be setup by the target eNB.

In this case, for a UE that performs handover to an RN, the handoverrequest message may be received by a DeNB. Here, the DeNB reads a targetcell ID from the message, finds a target RN that corresponds to thetarget cell ID, and forwards the message to the target RN.

Later, the target eNB transmits a handover request ACK to the MME (step,S1120). More particularly, after allocating resources required for allaccepted E-RAB, the target eNB may respond to the handover request ACKmessage. In this case, the handover request ACK message may include asuccessfully established E-RAB, an E-RAB of which setup is failed andinformation in relation to a radio interface (e.g., a handover commandfor the UE).

In the case that there is no available resource on an aspect of atarget, the target eNB responds with a handover failure message, thatis, transmits a handover failure message to the MME, instead oftransmitting the handover request ACK message (step, S1130).

Hereinafter, the paging will be described.

FIG. 12 is a flowchart schematically illustrating a procedure of paging.

Referring to FIG. 12, a UE may receive a paging message from a network(step, S1210).

More particularly, an object of the procedure that the UE receives apaging message may be,

-   -   for a transmission of paging information to the UE, when the        network is in an RRC idle state and/or    -   for informing a change of system information for the UEs in an        RRC idle state and the UEs in an RRC connected state by the        network, and/or    -   for informing an ETWS primary notification and/or an ETWS        secondary notification by the network, and/or    -   for informing a CMAS notification by the network.

The paging information may be provided to a higher layer (e.g., NAS).

The network may initiate the paging procedure by transmitting a pagingmessage on a paging occasion of the UE. In addition, the network mayaddress the paging message to a plurality of UEs by including a pagingrecord for each of the UEs in the paging message. Likewise, the networkmay indicate a change of the system information and/or provide an ETWSnotification or a CMAS notification through (or based on) the pagingmessage. The paging occasion may also be written as a paging time, andthe paging time may include information indicating one or more radioframe numbers and one or more subframe numbers or an index indicatingthe radio frame and the subframe.

Hereinafter, the present invention will be described in detail.

Recently, owing to the development of the information communicationindustry, a user may have a variety of terminals simultaneously. Forexample, the case is increasing that a user has a smart phone and asmart watch, a user has a smart phone and a tablet PC, or a user has asmart watch and a tablet PC.

Each of a plurality of UEs possessed by a user may have a capability ofperforming a cellular operation. That is, each of a plurality of UEs mayhave a capability of performing a communication with an eNBindependently. However, in the case that all of the UEs perform theprocedure for each of the conventional cellular operations, an operationtime of a UE of which battery capacity is relatively small is shorterthan an operation time of a UE of which battery capacity is relativelygreat. For example, in the case that a user has both of a smart phoneand a smart watch, and both of the smart phone and the smart watchperform the cellular operation and assuming that the amount of powerconsumed are the same, a battery of the smart watch of which batterycapacity is smaller than that of the smart phone is discharged fast, andaccordingly, the function of the smart watch is not fully fulfilled.

In the case that a plurality of UEs is proximate with each other as thecase that a user has all of the UEs, a plurality of the UEs undergoessimilar channel environment with respect to a specific network node(e.g., an eNB) that is going to communicate with. In addition, asdescribed above, a plurality of the UEs has the common feature. In theconventional art, even in the case that each of a plurality of the UEsthat is going to perform the cellular communication operation is in asimilar channel environment, each of a plurality of the UEs performs allprocedures (e.g., mobility procedure, paging procedure, handoverprocedure, scheduling procedure, etc.) that are required for theoperation of the cellular communication. In addition, the UEs performthe cellular communication procedure independently without consideringthe characteristics that the UEs provide a communication service to thesame user.

In the case that a plurality of UEs provides a communication service tothe same user or a plurality of UEs undergoes the similar channelenvironment, it is available for a specific UE among a plurality of theUEs to act as a proxy for the cellular communication procedure thatother UE should perform. Particularly, when a capability of each of theUEs, for example, a processing power and/or battery capacity/residualbattery amount is different, it is preferable for a UE that has enoughcapability acts as a proxy for the cellular communication procedure of aUE that has insufficient capability. As an example, it may be consideredthat the UE of great battery total capacity or residual battery capacityacts as a proxy for a part of the cellular procedure that should beperformed by a UE of small battery total capacity or residual batterycapacity.

Hereinafter, a method is proposed for guaranteeing a service qualitythat a user requires while minimizing the power consumption consumed byUEs when performing a cooperative communication between UEs (coordinatedTx/Rx), in the case that at least one of the following conditions aresatisfied: 1) a user has a plurality of UEs, 2) a plurality of UEs islocated normally proximate distance, 3) each of a plurality of UEssupports the cellular communication, 4) each of a plurality of UEs mayperform the cellular communication when the cellular communication isrequired, 5) in the proximate range, a plurality of UEs supports thetechnique (e.g., WLAN or Bluetooth or sidelink communication based onLTE), which is able to perform a communication between a plurality ofUEs with relatively low power in comparison with the cellularcommunication, 6) a battery capacity of a specific UE is small among aplurality of UEs and sensitive to the power consumption. As an exampleof the method, a method is proposed that a UE of which battery totalcapacity/residual battery capacity is relatively great acts as a proxyfor a part of the cellular procedure of a UE of which battery totalcapacity/residual battery capacity is relatively small.

For example, in the case that UE 1 is a device (smart watch) of whichbattery capacity is small and UE 2 is a device (smart phone) of whichbattery capacity is great, a method and apparatus is to be proposed thatUE 2 acts as a proxy for a procedure required for the cellularcommunication (transmission/reception) with a network and the cellularmanagement in place of UE 1 such that UE 1 may operate in the powersaving mode in an RRC connected mode with the aid of UE 2. Hereinafter,the process that UE 2 acts as a proxy for the cellular procedure for UE1 may be called that UE 2 provides a proxy-operation or aproxy-operation service to UE 1.

Hereinafter, for the convenience of description, the UE provided withthe proxy-operation service from another UE is named as “a first UE” or“UE 1”, and the UE that provides the proxy-operation service to anotherUE is named as “a second UE or “UE 2”. As described above, the second UEmay be a UE of which battery capacity/residual capacity is relativelygreater than that of the first UE, or a UE of which computation capacityis relatively superior to that of the first UE. In addition,hereinafter, for the convenience of description, it will be describedthat the second UE acts as a proxy for the operation of the first UE.However, it is understood that this is just for the convenience ofdescription, and the operation that the first UE acts as a proxy for theoperation of the second UE is not excluded in the scope of the presentinvention.

FIG. 13 is a flowchart for a procedure of determining a proxy-operationperformance according to an embodiment of the present invention.

Referring to FIG. 13, a first UE operates in a normal mode (step,S1310). Here, the fact that the first UE operates in a normal mode maymean that the first UE is on performing a general procedure for thecellular communication (e.g., mobility procedure, paging procedure,handover procedure, scheduling procedure, etc.).

The second UE may determine to act as a proxy for the procedure inrelation to the cellular communication of the first UE, that is, toperform a proxy-operation (may also be referred as an agent operation).As described above, it may be called that the second UE provides aproxy-operation/proxy service to the first UE, or it may be representedthat the second UE performs a proxy-operation for the first UE. Theproxy-operation/proxy service may be referred as the second UE transmitsand receives a signal of the first UE in place of the first UE. In thetransmission and reception proxy of a signal, the signal of the first UEmay mean a signal that an eNB is going to transmit to the first UE (likethe conventional art) in the aspect of UE-dedicated signaling ofdownlink. The signal of the first UE may mean a signal of an eNB thatthe first UE should be measured for the connection management or thelink quality measurement generally (like the conventional art) in theaspect of broadcast/common signaling of downlink. In the transmissionand reception proxy of a signal, the signal of the first UE may mean asignal that the first UE is going to transmit to an eNB through commonsignaling or UE-dedicated signaling (like the conventional art) in theaspect of uplink. That is, in the transmission and reception proxy of asignal, the signal may include at least one of a control signal anddata.

Here, the procedure of determining the proxy-operation may be triggeredby the first UE or the second UE. For example, the second UE maybroadcast the proxy operation information to at least one neighboring UEor may transmit the proxy operation information to a specific (orappointed) UE such as the first UE (step, S1320). In this case, theoperation that the first UE receives the proxy operation informationfrom the second UE is not an essential process of the present invention,but the first UE may transmit a proxy-operation request to the second UEby its own determination of the first UE. That is, the proxy-operationof the second UE may be triggered by the first UE.

The proxy operation information may include a factor representingwhether the proxy-operation service is available, an identity of thesecond UE or a user code of the second UE, a service/application code inwhich the proxy operation is available to be provided, a type of directcommunication link supportable, serving cell information of the secondUE, and the like.

The first UE may determine whether the second UE is able to provide theproxy-operation service to the first UE itself based on the UEidentity/user code/service code included in the received proxy operationinformation.

For example, the first UE may determine whether the second UE is able toprovide the proxy-operation service to the first UE itself based on theUE identity/user code/service code included in the proxy operationinformation. The first UE may identify whether the second UE is a UEproper to provide the proxy-operation service by sending an inquirythrough information stored in advance or to a network (e.g.,proxy-operation service server existed in a network).

In the case that a service code is included in the proxy operationinformation, the first UE may operate as follows. When the service codethat corresponds to a service that the first UE provides to a user isincluded in the received proxy operation information, the first UE mayregard the second UE as a UE proper to provide the proxy operationservice.

The direct communication link that is supportable in the proxy operationinformation means the communication link information used whenexchanging message/data between UEs for the proxy operation service.Types of the direct communication link may include the communicationlinks supported among the operation of Wi-Fi type (802.11 type), ZigBeetype (802.15.4 type), Bluetooth type, sidelink in LTE-based licensedband and sidelink in LTE-based unlicensed band. For each communicationlink, the detailed parameter/capability information of the link may beprovided, which is required for a connection between UEs of thecorresponding link. In the case that a plurality of direct communicationlinks is indicated, a priority value of each communication link may beindicated together. As serving cell information of the second UE, aserving cell identifier and a PLMN ID list in which the serving cell isbelonged may be provided.

The proxy-operation information may be transmitted to a neighboring UEwith being encrypted (e.g., with an integrity protection) or togetherwith a digital signature. The first UE receives the proxy-operationinformation and decrypts and verifies the received information accordingto the encryption, and may perform the proxy-operation through thesecond UE only in the case that the information is verified.

After receiving the proxy-operation information, the first UE maytransmit a message (proxy-operation performance request message)requesting to performing the proxy-operation to the second UE (step,S1330). As described above, the first UE may transmit theproxy-operation performance request message to the second UE afterreceiving the proxy-operation information. Otherwise, even in the casethat the first UE fails to receive the proxy-operation information, thefirst UE may transmit the proxy-operation performance request message tothe second UE with its own determination of the first UE.

Here, the proxy-operation performance request message may be i) directlytransmitted to the second UE, ii) transmitted to the second UE throughan eNB, or iii) transmitted to the second UE through an MME. Theproxy-operation performance request message may be transmitted to thesecond UE through a direct communication link between UEs. An example ofthe direct communication link is one of Wi-Fi type (802.11 type), ZigBeetype (802.15.4 type), Bluetooth type, sidelink in LTE-based licensedband and sidelink in LTE-based unlicensed band. Generally, the first UEmay select a preferable link among the direct communication links. Adetermination of the preference among links may be according to thedetermination of an inner part of the first UE based on a link prioritystored in the first UE in advance, a user configuration or at least oneof the QoS of the service provided by the first UE and the residualbattery capacity situation. In the case that the second UE notifies thepreference among the direct communication links to the first UE already,the first UE may use the communication link that the second UEdesignates as the highest priority. The detailed example that theproxy-operation performance request message is transmitted to the secondUE through an eNB or an MME will be described below.

For the proxy-operation performance request, the first UE may forwardthe following information to the second UE or a network node (e.g., aneNB or an MME, an HSS or a proxy-operation service server). In the casethat the following information is forwarded to a network node, theinformation may be forwarded to the network node through the second UE.The information of the proxy-operation performance request may include auser code of the first UE, a user code of the second UE, a service codethat the first UE wishes to be provided with the proxy-operation, a userpreference, pre-configuration for the proxy-operation of the first andsecond UEs, a type of direct communication link usable between the firstUE and the second UE, a direct link quality between first UE and thesecond UE, a signal reception quality of a specific cell measured by thefirst UE, a serving cell identifier of the first UE, and the like. Basedon the information, it may be determined whether the proxy-operationperformance request is accepted. The method of determining whetherproxy-operation performance request is accepted includes 1) a methodthat the second UE determines whether to accept it finally and notifiesthe determination to a network and 2) a method that a network determineswhether to accept it finally and notifies the acceptance to the secondUE.

More particularly, in order to request the proxy-operation performanceto the second UE or a network node (e.g., an eNB or an MME, an HSS or aproxy-operation service server), the first UE may transmit at least oneof the following information.

-   -   User preference information of the first UE: For example, a user        of the first UE may prefer the proxy-operation through the        second UE. That is, in the case that the first UE (smart watch)        and the second UE (smart phone) are possessed by the same user,        the user may prefer that the second UE acts as a proxy for the        operation of the first UE, which may be notified to the second        UE by the first UE.    -   A user identifier/code of the first UE and/or a user        identifier/code of the second UE. A UE or a network node that        receives a user identifier/code to which the first UE is        belonged and/or a user identifier/code to which the second UE is        belonged may identify that the proxy-operation service        performance is proper based on the information stored in advance        or by performing an inquiry to the proxy-operation service        server. The user identifier/code of the UE may be allocated from        a network (e.g., MME) in a procedure that each UE registers in a        cellular network or a subsequent procedure (i.e., Non-Access        Stratum procedure), or may be allocated from a network (e.g.,        proxy-operation service server) through a separate proxy        operation preparation procedure that may be performed before the        procedure of the proxy operation performance request-acceptance.    -   A service code that the first UE wishes to be provided with the        proxy-operation/a service code that the second UE may provide        the proxy operation. Based on the information, it may be        determined whether it is proper or not to provide a proxy        operation service in relation to a specific service between two        UEs. The identifier/code corresponding to each service may be        allocated from a network (e.g., MME) in a procedure that a UE        registers in a cellular network or a subsequent procedure (i.e.,        Non-Access Stratum (NAS) procedure), or may be allocated from a        network (e.g., proxy-operation service server) through a        separate proxy operation preparation procedure that may be        performed before the procedure of the proxy operation        performance request-acceptance.    -   Pre-configured association information of the first UE and the        second UE (i.e., the information indicating that the first UE        and the second UE are associated for the operation of the        present invention. For example, it may be identified that there        may be the pre-configured association between the UEs of the        same user or the UEs of different users included in the same        user group.).    -   A type of direct communication link supported between the first        UE and the second UE. An example of the direct communication        link is one of Wi-Fi type (802.11 type), ZigBee type (802.15.4        type), Bluetooth type, sidelink in LTE-based licensed band and        sidelink in LTE-based unlicensed band. A network may designate a        specific communication link or provide a usable communication        link list to a proxy operation provider/receiver UE using the        direct communication link that may be used for the proxy        operation.    -   Link quality information between the first UE and the second UE        measured by the first UE. For example, the second UE may        transmit a reference signal or data to the link or the first UE        may measure a reception quality of the reference signal and        notify it to the second UE. For this, the second UE may        broadcast the reference signal used for a measurement        periodically. Here, the link quality may mean a sidelink link        quality. As another example, the link may be a link quality of        Wi-Fi (e.g., measured Received Signal Strength Indicator        (RSSI)).    -   A reception quality of a signal such as RSRP/RSRQ of a specific        cell measured by the first UE. For example, the first UE may        measure a reception quality of a signal targeted to the cell        designated by its own serving cell or the second UE (e.g., a        serving cell of the second UE) and notify it to the second UE.    -   Serving cell information of the first UE (e.g., a serving cell        ID of the first UE) and PLMN information (e.g., R-PLMN ID that        the first UE registers or selected PLMN ID)    -   An RRC state of the first UE. For example, it may be identified        whether the state is an RRC_IDLE or an RRC CONNECTED.    -   A proxy operation procedure list that the first UE wishes to be        provided. The proxy operation procedure list means a list that        notifies the proxy operation procedure that the first UE wishes        to be provided from the second UE among the procedures that the        first UE is required to perform the cellular communication. For        example, the list may indicate a paging procedure proxy, a        scheduling monitoring proxy, a data transmission and reception        proxy (particularly, it is available to be specifically        indicated such as a transmission only proxy, a reception only        proxy, and transmission and reception proxy, etc.), a control        message transmission and reception proxy (it is also available        to particularly indicate such as an RRC message transmission and        reception proxy, a NAS message transmission and reception proxy,        etc.), a mobility procedure proxy (it is also available to        particularly indicate such as an idle mode mobility proxy, a        connected mode mobility proxy, etc.).    -   A proxy operation procedure list that the second UE may provide.        This list means a list that notifies a proxy operation that the        second UE may provide to the first UE such that the first UE may        perform the cellular communication through the second UE. An        example of the proxy operation that may be included in the list        is the same as that of the proxy operation included in the proxy        operation procedure list that the first UE wishes to be        provided.

In response to the proxy operation performance request, the first UEreceives a proxy operation performance acceptance message from thesecond UE (step, S1340). The proxy operation performance acceptancemessage (i.e., a message in response to the proxy operation request) mayinclude the following information.

-   -   A service code that the second UE is decided to provide for the        proxy operation.    -   A type of direct communication link between the first UE and the        second UE used for the proxy operation and a link configuration        parameter.    -   Link quality information between the first UE and the second UE        measured by the second UE.    -   A reception quality of a signal such as RSRP/RSRQ of a specific        cell measured by the second UE.    -   Serving cell information of the second UE (e.g., a serving cell        ID of the first UE) and PLMN information (e.g., R-PLMN ID that        the first UE registers or selected PLMN ID)    -   An RRC state of the second UE.    -   A proxy operation procedure list that the second UE determines        to provide.

As described above, in the case that performing of the proxy operationis determined through signaling between UEs, either one of the UEs(i.e., the first UE or the second UE) among the UEs associated with theproxy operation may notify that performing of the proxy operation isdetermined to a network.

-   -   For example, the second UE that is going to act as a proxy for        the mobility procedure may notify that the second UE is going to        act as a proxy for the mobility procedure of the first UE to its        own serving cell. In this case, the eNB belonged to the serving        cell of the second UE may request and receive the UE context of        the first UE (e.g., the UE capacity of the first UE), the        service information of the first UE and the bearer configuration        information (including QoS parameter) of the first UE to a        serving cell eNB of the first UE or an MME that corresponds to        the R-PLMN of the first UE.    -   As another example, the second UE that is going to act as a        proxy for the mobility procedure may notify that the second UE        is going to act as a proxy for the mobility procedure of the        first UE to its own serving CN (e.g., MME) through a NAS        message. In this case, the CN node may make the UE context of        the second UE include the UE context of the first UE. That is,        the UE context of the second UE may be updated to further        include the UE context of the first UE, and the updated UE        context of the second UE may be transmitted to the eNB of the        second UE (according to this scheme, a change of the eNB may be        minimized.

The network that determines to do the proxy operation between the firstUE and the second UE (or the network that identifies that the proxyoperation between the first UE and the second UE is determined) mayselect an appropriate cell for the proxy operation. In this case, forexample, the network may select an optimal serving cell by reference tothe information included in the proxy operation performance requestmessage described above, the measurement report transmitted by thesecond UE, the R-PLMN and/or Selected PLMN of the first UE and thesecond UE, and the like.

When a cell for the proxy operation is determined, the network maycommand the first UE to perform handover or cell reselection and makethe first UE move to the corresponding cell, and may also command thesecond UE to perform handover and to move to the corresponding cell.Through this, the first UE and the second UE may be connected with thesame PLMN/MME and the same serving cell.

Later, a message information forwarding interface is setup between thefirst UE and the second UE (step, S1350).

More particularly, to the second UE that provides the proxy operationservice to the first UE, an additional radio bearer (i.e., a radiobearer for transmitting traffic accompanied by the proxy operation) maybe configured. The configuration for an additional radio bearer betweenthe second UEs may also be based on an RRC message received from thenetwork. According to a network configuration, the additional radiobearer may be configured dedicated to the proxy operation but may alsobe configured so as to be used for a transmission of data traffic of thesecond UE. The network may reconfigure a specific bearer among thepreconfigured radio bearers so as to transmit the traffic accompanied bythe proxy operation.

Here, the additional radio bearer configuration may be divided into Uuinterface between an eNB and a UE and PC5 interface between UEs. Thesecond UE may also construct an additional layer 2 entity and anadditional channel (e.g., physical channel, transport channel or logicalchannel) with respect to each of the additional radio bearerconfigurations.

For a proxy radio bearer configuration in the Uu interface between aneNB and a UE, the network may also configure an Evolved packet system(EPS) bearer corresponding to the second UE. The EPS bearer is mapped tothe proxy radio bearer for the first UE, and the second UE may relay abearer service corresponding to the first UE by being setup to thesecond UE. At this point, the CN may identify the proxy radio bearer,that is, the additional radio bearers are associated with the proxyoperation of the second UE. In this case, the eNB may notify that theadditional radio bearer is the proxy radio bearer to the second UE. TheCN may discriminate the priority of the proxy radio bearer and a normalradio bearer. In this case, the discrimination of the priority may bebased on the scheme of newly determining a value of QoS Class Identifier(QCI) or Allocation and Retention Priority (ARP) or the scheme ofdefining new QoS parameter. Alternatively, in order to share the factthat the bearer is the proxy operation service between an MME and aneNB, it may considered to introduce a new flag (may be an indicatorconstructed as 1 bit) mapped to the bearer configuration information orto perform signaling of the flag between an eNB and an MME.

As described above, in the case that additional radio bearers for thefirst UE are configured for the second UE, the second UE may notify theradio bearer configuration described above to the first UE, and throughthis, the first UE may configure an additional radio bearer.

The radio bearer added to the second UE may include a radio bearerconstructed in the Uu interface, which is a communication interfacebetween an eNB and a UE and a radio bearer constructed in the inter-UEdirect communication interface between the second UE and the first UE.The inter-UE direct communication interface may include an inter-UEdirect communication interface based on LTE, that is, PC5 interface(sidelink). In this case, the first UE may configure a Sidelink RadioBearer for the PC5 interface. Here, when the first UE configures thedirect communication link for the proxy operation or the radio bearerfor the proxy operation with the second UE, the first UE may release thecorresponding radio bearers in the Uu interface. The release of thebearers may be performed by an instruction of an eNB or a determinationof the UE itself, after the configuration of the inter-UE directcommunication link for the proxy operation or the radio bearer iscompleted.

In addition, the first UE may transmit UE configuration information ofthe first UE to the second UE. The configuration information may includea physical layer configuration, a MAC configuration, an RLCconfiguration and a PDCP configuration of the UE. The second UE thatreceives the UE configuration information may use the information forperforming the proxy operation. For example, in order for the second UEto receive downlink data in place of the first UE and/or to transmituplink data in place of the first UE, it may be required for the secondUE to construct an RLC entity and a PDCP entity of the second UEaccording to the RLC, PDCP configuration of the first UE.

In order for the second UE to receive downlink data in place of thefirst UE and/or to transmit uplink data in place of the first UE, it isalso available for the second UE to construct an additional MAC entityaccording to the MAC configuration of the first UE and to construct anadditional PHY configuration according to the PHY configuration of thefirst UE.

Later, the first UE enters a proxy service mode state (step, S1360). Theproxy service mode may be referred to as a mode that omits a part or amost part of the procedure performed by a UE in a normal mode. Forexample, the first UE performs a paging procedure, a schedulingmonitoring, a data transmission and reception, and the like in thenormal mode, but may not directly perform at least one of the operationsin the proxy service mode. In this case, the operation not directlyperformed by the first UE may be worked by the second UE. Accordingly,the power consumption of the UE in the proxy service mode is smallerthan that of the UE in the normal mode, generally. Therefore, the proxyservice mode may also be called a power saving mode. Hereinafter, forthe convenience of description, the proxy service mode may be referredto as the power saving mode. The power saving mode (i.e., proxy servicemode) may be implemented in the form that the second UE acts as a proxyfor a part (or the whole) of the procedure for the cellularcommunication for the first UE or that the first UE omits or performwith a low frequency a part (or the whole) of the procedure for thecellular communication, and the state itself for performing theoperation may also be referred to as the power saving mode.

More particularly, the first UE, when the second UE is going to performthe proxy operation procedure for the first UE, may operate in the powersaving mode according to an indication of the second UE or an indicationof an eNB or an MME. Here,

1) In the case that the first UE is in an RRC connected mode,

The UE in the RRC connected state (or mode) may omit or perform with alow frequency the operations that the first UE should perform in thenormal RRC connected mode, while the first UE is in the power savingmode (i.e., proxy service mode). For example,

-   -   The first UE may not perform a measurement of a serving cell        and/or a neighboring cell, which is required for the mobility        support.    -   The first UE may omit the measurement report procedure which is        required for the mobility support. That is, the UE may omit the        evaluation of a measurement report event and the resulted        measurement report.    -   The first UE may perform a measurement of a serving cell and/or        a neighboring cell, which is required for the mobility support        with a low frequency in comparison with the second UE.    -   The first UE may not perform a control channel monitoring which        is required for the mobility support.    -   The first UE may perform a control channel monitoring which is        required for the mobility support with a low frequency in        comparison with the second UE.    -   The first UE may not perform a control channel monitoring which        is required for downlink scheduling.    -   The first UE may omit a paging reception for maintaining an SIB        as the latest state in the connected mode.    -   The first UE may omit a paging reception for receiving an urgent        message in the connected mode.    -   The first UE may omit a Radio Link Monitoring (RLM) procedure        for determining that a use of the RRC connection is usable.

2) In the case that the first UE is in an RRC idle mode,

The UE in the RRC idle mode may omit or perform with a low frequency theoperations that the first UE should perform in the normal RRC idle mode,while the first UE is in the power saving mode. For example,

-   -   The first UE may not perform a measurement of a serving cell        and/or a neighboring cell, which is required for the mobility        support.    -   The first UE may perform a measurement of a serving cell and/or        a neighboring cell, which is required for the mobility support        with a low frequency in comparison with the second UE.    -   The first UE may omit an evaluation of cell selection/cell        reselection which is required for the mobility support and the        consequential cell selection/cell reselection.    -   The first UE may omit a paging reception for maintaining an SIB        as the latest state in the idle mode.    -   The first UE may omit a paging reception for receiving a        disaster message (e.g., ETWS, commercial mobile alert system        (CMAS) and Korean Public Alert System (KPAS)) in the idle mode.

In addition, while the first UE is in the power saving mode, the firstUE may be switched from the RRC connected mode to the RRC idle mode, mayoperate in the power saving mode, or may monitor a downlink channelaccording to the ‘Extended DRX cycle’ which is more extended than theDiscontinuous Reception (DRX) cycle which is currently configured.

For the power saving mode operation of the first UE, a network maytransmit an RRC message to the first UE and the second UE, and mayconfigure the following parameter values. In this case, the network maytransmit the RRC message directly to the first UE or may transmit theRRC message to the first UE through the second UE.

-   -   Timer value for the power saving mode: In the case of receiving        the parameter value from the network, the first UE may start the        timer when receiving the power saving mode, and may be switched        from the power saving mode to the normal mode when the timer        expires. The second UE may also drive the timer, and may        determine whether the first UE is in the power saving mode. For        example, in the case that the first UE enters the power saving        mode, the second UE may start the timer which is the same as the        timer started in the first UE. Later, when the timer in the        second UE expires, the second UE may determine the timer of the        first UE to be expired too. Accordingly, the second UE may also        determine whether the first UE enters the normal mode from the        power saving mode. In the case that the first UE does not        receive the parameter value from the network, the first UE (or        the second UE) may setup the timer value as being infinite. In        this case, the first UE may maintain the power saving mode until        receiving a separate information (or message).    -   Paging DRX cycle in the power saving mode: In the case of        receiving the parameter value from the network, the first UE may        monitor paging according to the parameter value when the first        UE in the RRC idle state enters the power saving mode.    -   Long/short DRX cycle in the power saving mode: In the case of        receiving the parameter value from the network, the first UE may        perform the DRX according to the parameter value when the first        UE in the RRC connected state enters the power saving mode.    -   Configuration and specific parameter indicating the procedure        that the first UE should perform even after entering the power        saving mode, or the procedure that the first UE may omit or        perform in a low frequency.

FIG. 14 is a flowchart for a procedure of determining a proxy-operationperformance according to another embodiment of the present invention.

Referring to FIG. 14, a first UE operates in a normal mode (step,S1410). As described above, the fact that the first UE operates in anormal mode may mean that the first UE is on performing a generalprocedure for the cellular communication (e.g., mobility procedure,paging procedure, handover procedure, scheduling procedure, etc.).

The second UE may broadcast the proxy operation information to at leastone neighboring UE or may transmit the proxy operation information to aspecific (or appointed) UE such as the first UE (step, S1420). In thiscase, the details that the first UE receives the proxy operationinformation from the second UE are as described above.

After the first UE receives the proxy operation information from thesecond UE, or after the first UE itself determines even in the case thatthe first UE does not receive the proxy operation information from thesecond UE, the first UE may transmit a request message for the proxyoperation performance to an eNB (step, S1430).

Later, the eNB transmits a proxy operation performance request messageto the second UE (step, S1440).

In response to the proxy operation performance request, the second UEtransmits a proxy operation performance acceptance message with theinformation of a message information forwarding interface between UEs tothe eNB (step, S1450).

Later, the eNB transmits a proxy operation performance acceptancemessage with the information of a message information forwardinginterface between UEs (step, S1460).

As described above, when the proxy operation performance is determinedthrough signaling between UEs, a UE (i.e., the first UE or the secondUE) among the UEs associated with the proxy operation may notify thatthe performance of the proxy operation is determined to the eNB, and thedetailed examples of the notification that the performance of the proxyoperation is determined to the eNB are as described above.

Later, a message/data information forwarding interface is setup betweenthe first UE and the second UE (step, S1470). In this case, the detailedexamples of the message/data information forwarding interface setupbetween the first UE and the second UE are as described above.

Later, the first UE enters the state of saving power, that is, operatesin the power saving mode (step, S1480). Here, the detailed examples ofthe power saving mode are as described above.

FIG. 15 is a flowchart for a procedure of determining a proxy-operationperformance according to still another embodiment of the presentinvention.

Referring to FIG. 15, a first UE operates in a normal mode (step,S1510). As described above, the fact that the first UE operates in anormal mode may mean that the first UE is on performing a generalprocedure for the cellular communication (e.g., mobility procedure,paging procedure, handover procedure, scheduling procedure, etc.).

The second UE may broadcast the proxy operation information to at leastone neighboring UE or may transmit the proxy operation information to aspecific (or appointed) UE such as the first UE (step, S1520). In thiscase, the details that the first UE receives the proxy operationinformation from the second UE are as described above.

After the first UE receives the proxy operation information, or afterthe first UE itself determines even in the case that the first UE doesnot receive the proxy operation information, the first UE may transmit arequest message for the proxy operation performance to a network node(e.g., a proxy operation service server or an MME) (step, S1530).

Later, the network node transmits a proxy operation performance requestmessage to the second UE (step, S1540).

In response to the proxy operation performance request, the second UEtransmits a proxy operation performance acceptance message with theinformation of a message information forwarding interface between UEs(step, S1550).

Later, the network node transmits a proxy operation performanceacceptance message with the information of a message informationforwarding interface between UEs (step, S1560).

As described above, when the proxy operation performance is determinedthrough signaling between UEs, a UE (i.e., the first UE or the secondUE) among the UEs associated with the proxy operation may notify thatthe performance of the proxy operation is determined to the eNB, and thedetailed examples of the notification that the performance of the proxyoperation is determined to the eNB are as described above.

Later, a message information forwarding interface is setup between thefirst UE and the second UE (step, S1570). In this case, the detailedexamples of the message information forwarding interface setup betweenthe first UE and the second UE are as described above.

Later, the first UE enters the state of saving power, that is, operatesin the power saving mode (step, S1580). Here, the detailed examples ofthe power saving mode are as described above.

FIG. 16 illustrates a communication method performed by the second UEaccording to an embodiment of the present invention.

Referring to FIG. 16, the second UE may determine to perform a signaltransmission and reception proxy operation for the first UE (step,S1610). The determination procedure is as described above with referenceto FIG. 13 to FIG. 15.

The second UE receives the signal of the first UE transmitted from anetwork (step, S1620).

The second UE forwards the signal of the first UE to the first UE (step,S1630).

The second UE transmits the signal received from the first UE to thenetwork (step, S1640).

Referring to FIG. 16, the second UE may monitor the control informationthat the network transmits to the first UE. In addition, the second UEmay receive the data that the network transmits to the first UE. In thiscase, the control information that the network transmits to the first UEmay be identified by an identifier of the first UE. For example, thecontrol that the network transmits to the first UE may be monitored in asearch space indicated by the identifier of the first UE. That is, thesecond UE monitors the control information transmitted to the first UEusing the identifier of the first UE. In order to enable this, thesecond UE may receive the identifier of the first UE from the network orthe first UE in advance.

Alternatively, the control information that the network transmits to thefirst UE may be identified by an identifier of the second UE. In thiscase, the control information that the network transmits to the first UEmay include a field representing that the control information is withrespect to the first UE.

In the case that the second UE receives the data that the networktransmits to the first UE, the second UE may forward the data to thefirst UE. The data may be either one of a higher layer messagetransmitted through a signaling radio bearer (SRB) and a user datatransmitted through a data radio bearer (DRB).

The second UE may provide the information representing whether the datais a higher layer message transmitted through an SRB and a user datatransmitted through a DRB to the first UE.

Using the uplink resource allocated to the first UE by the network, thesecond UE may transmit the uplink data of the first UE.

The second UE may request the uplink resource for the first UE to thenetwork, and may transmit the uplink data of the first UE using theuplink resource allocated from the network by the request.

In the case that the second UE determines to act as a proxy for thesignal transmission and reception of the first UE, the first UE mayoperate in the power saving mode. In the power saving mode, the first UEmay not perform a measurement of a serving cell and a neighboring cellwhich is required for performing a procedure in relation to themobility, may perform the measurement of a serving cell and aneighboring cell which is required for performing a procedure inrelation to the mobility with a lower frequency than the second UE, mayomit a paging reception, or may perform the paging reception with alower frequency than the second UE. The second UE may be a UE of whichbattery capacity is greater than that of the first UE.

The second UE may receive the configuration information of the first UEfrom the first UE, and may act as a proxy for the signal transmissionand reception of the first UE based on the configuration information.

Now, each step of the FIG. 16 will be described in detail.

Assuming the case that the second UE determines to perform a proxyoperation, that is, to receive a signal for the first UE in place of thefirst UE, the second UE may monitor a downlink control channel that thenetwork is going to transmit to the first UE. The downlink controlchannel may be a physical downlink control channel (PDCCH), for example.

One of the following methods may be used for the second UE to monitorthe downlink control channel for scheduling of the first UE.

First, the second UE may monitor the downlink control channel of thefirst UE using its own identifier. In the case that the downlink controlchannel is for downlink scheduling (e.g., PDCCH), the eNB may performthe downlink scheduling of the first UE using the identifier of thesecond UE. For example, a PDCCH for a specific UE may include anidentifier of the specific UE, for example, downlink control information(DCI) to which Cyclic Redundancy Check (CRC) masked by a cell—RadioNetwork Temporary Identifier (C-RNTI) is added. The eNB may add themasked CRC as an identifier of the second UE to the DCI included in thePDCCH for the first UE. The PDCCH for the first UE (more particularly, aDCI for the first UE) may not include a separate field representing thatthe PDCCH is for scheduling of the first UE. A physical layer (PHY) ofthe second UE may operate by identifying that the scheduling for thefirst UE is the scheduling for the second UE. According to the firstmethod, there is an advantage that a change of layer 1 (PHY) of thesecond UE is minimized.

Second, the second UE may monitor the downlink control channel of thefirst UE using an identifier of the first UE. In this method, the eNBperform downlink scheduling of the first UE using the identifier of thefirst UE.

Particularly, the second UE monitors a UE-specific search space set tothe first UE in addition to the common search space. In addition, thesecond UE monitors the PDCCH distinguished by an identifier (e.g.,C-RNTI) of the first UE.

In addition, the second UE may give higher priority for monitoring thePDCCH for the second UE itself than for monitoring the PDCCH for thefirst UE, or on the contrary, may give higher priority for monitoringthe PDCCH for the first UE than for monitoring the PDCCH for the secondUE itself. The priority for monitoring the PDCCH may be determinedaccording to the priority determined between the first and second UEs orthe priority of the service provided by the first and second UEs.

Third, the second UE may monitor the downlink control channel of thefirst UE using its own identifier, but uses a field representing that itis the downlink control channel of the first UE. In the case of usingthis method, the eNB performs downlink scheduling using the identifierof the second UE, but adds a field representing that the PDCCH (moreparticularly, a DCI for the first UE) is for the first UE in the PDCCHfor the first UE. The field may indicate an index for the first UE or anID of the first UE. After the second UE detects the PDCCH for the firstUE using its own C-RNTI, the second UE may distinguish whether the PDCCHis for the first UE or the second UE through the field. This method maybe called cross-UE scheduling.

In addition, the second UE determines to perform a proxy operation, thatis, to receive a signal for the first UE in place of the first UE, thesecond UE may monitor a data channel that the network is going totransmit to the first UE. The data channel may be a physical downlinkshared channel (PDSCH).

The eNB, the first UE and the second UE may setup a proxy radio bearerfor the proxy operation. The proxy radio bearer may be divided into asignaling radio bearer (SRB) and a data radio bearer (DRB), and separateSRB and DRB may be setup for the proxy operation. The separate SRB andDRB may be distinguished in Layer 2 by being distinguished through aseparate logical channel identity (LCID) reserved for a use of the proxyradio bearer or including a new field indicating that a MAC SDU is thedata corresponding to the proxy radio bearer in a MAC subheader.

When the second UE performs a Logical Channel Prioritization formultiplexing a logical channel in an uplink transmission, the eNB, thefirst UE and the second UE may give a specific priority for the proxyradio bearer. For example, the proxy signaling radio bearer (Proxy SRB)may have lower priority than the existing SRB0, SRB1 and SRB2 or may besetup as the priority as the same as SRB2 (priority of SRB2 is lowerthan that of SRB1 and SRB0). When the proxy SRB is generated, the secondUE may determine the priority of the Proxy SRB autonomously. As anotherexample, the proxy signaling radio bearer (Proxy SRB) may have thepriority such as the lowest priority among the existing DRBs or may havea specific lower priority than the priority of the existing DRBs.Basically, the priority of the Proxy DRB also follows the priority valueindicated by a network like other DRBs. The eNB may differently setupthe priority of the logical channels such that the first and second UEsmay process the separate radio bearers by discriminating the priority ofthe existing radio bearers.

In the case that the second UE acts as a proxy for a data reception ofthe first UE, the second UE may act as a proxy for the PHY, MAC, RLC andPDCP operations that the first UE should perform when the first UEdirectly receives data from the eNB. The second UE may receive a datachannel for the first UE using a required configuration among the PHY,MAC, RLC and PDCP of the first UE. The second UE may operate as if theconfiguration required for the operation required for receiving dataamong the PHY, MAC, RLC and PDCP configurations of the first UE isconfigured by receiving from the eNB. That is, the second UE operates asif it is the first UE.

Or, in the case that the second UE acts as a proxy for a data receptionof the first UE, the second UE performs the proxy operation (acts as aproxy for the data reception) according to the PHY, MAC, RLC and PDCPconfigurations that may be used in the proxy operation, and performs thePHY, MAC, RLC and PDCP operations according to it.

Now, the process (step, S1630) will be described for forwarding a signalto the first UE by the second UE that receives the signal for the firstUE in place of the first UE in FIG. 16.

In the case that the second UE performing the proxy operation receivesthe data that should transmitted to the first UE from the network, thesecond UE may transmit the data to the first UE. The data that thesecond UE transmits to the first UE may be an RRC message transmittedthrough an SRB. Or, the data that the second UE transmits to the firstUE may be a user data (IP packet) transmitted through a DRB.

The data may be transmitted to the first UE directly from the second UEthrough an inter-UE direct communication link (i.e., using D2Dcommunication) or may be transmitted through other communication node.For example, the data may be transmitted using a communication techniquethat may perform the information transmission between UEs with low powersuch as an inter-UE direct communication link using Wi-Fi, acommunication link between UEs using Bluetooth or a direct communicationlink between UEs using LTE/LTE-A.

The data transmitted to the second UE through an inter-UE direct linkfor the purpose of transmitting data to the network by the first UE maybe a MAC PDU, a RLC PDU, a PDCP PDU, or a PDU of PDCP higher layer(e.g., IP layer) of the first UE. When the second UE receives the datathrough the inter-UE direct link, the second UE determines to perform anuplink transmission by performing an additional a second sublayerprocessing by treating the data as an SDU of the second sublayer in thesecond UE depending on the fact that the received data is a PDU of acertain second sublayer.

FIG. 17 illustrates an example of transmitting data to the second UE bythe first UE.

The data that the first UE (UE1) transmits to the second UE (UE2) may bethe data that the first UE is going to transmit to a network. The firstUE may transmit data to the second UE through the inter-UE direct linksuch as Wi-Fi, ZigBee, Bluetooth, sidelink provided in LTE-A (ProSe),and the like. The first UE may transmit the data processed only to aspecific layer among its own protocol layers to the second UE. Forexample, the first UE may transmit the MAC PDU 173 that is the dataprocessed up to MAC layer, the RLC PDU 172 processed up to RLC layer,PDCP PDU 171 processed up to PDCP layer or higher layer PDU 170processed up to PDCH higher layer (e.g., IP layer) to the second UE.

The second UE that receives the data from the first UE may consider thelayer in which the received data is processed. And after processing thenext layer, second UE may transmit the data to the network. For example,when receiving a MAC PDU from the first UE, the second UE may transmitthe data after performing an additional processing the data in PHYlayer. When receiving a RLC PDU from the first UE, the second UE maytransmit the data after performing an additional processing the data inMAC and PHY layer sequentially.

Meanwhile, when the first UE forwards the data to the second UE, a linkconverter may add a control field that indicates a type of the data tothe data forwarded through the inter-UE direct link.

FIG. 18 illustrates an example of a protocol data unit (PDU) formatavailable to be used in an inter-UE direct link.

Referring to FIG. 18, the data forwarded through an inter-UE direct linkmay include a direct link header and contents. The contents part mayinclude the information (field) indicating that the data is a PDU of acertain L2 sublayer and/or the information (field) indicating a type ofthe forwarded data. For example, the contents may include fieldsindicated by L and T. The field indicated by L is the informationindicating that the data is a PDU of a certain L2 sublayer, and mayindicate whether the data is a MAC PDU, a RLC PDU, a PDCP PDU or a PDUof PDCP higher layer (e.g., IP). The field indicated by T may includethe information indicating a type of the data. The information mayindicate whether the data is a data transmitted through an SRB/controldata or a user data transmitted through a DRB. The R field may indicatewhether the data includes a specific MAC CE or at least one MAC CE. Or,the R field may indicate whether the data includes a specific RLCcontrol PDU or at least one RLC control PDU. Or, the R field mayindicate whether the data includes a specific PDCP control PDU or atleast one PDCP control PDU.

In order to act as a proxy for the transmission of the first UE, thelink converter of the second UE that receives the data from the first UEthrough the inter-UE direct link identifies that the received data is aPDU of a certain second sublayer, and determines to send the receiveddata to the second sublayer based on it. For example, when the receiveddata is a MAC PDU, this is sent to PHY, and when the received data is anRLC PDU, this is sent to MAC. In addition, when the received data is aPDCP PDU, this is sent to RLC, and when the received data is a PDU ofPDCP higher layer, this is sent to PDCP. The link converter of thesecond UE may identify the T control field, and may determine throughwhich radio bearer the received data is transmitted (in the case thatthe received data is a PDCP PDU) or through which logical channel thereceived data is transmitted (in the case that the received data is anRLC PDU), and so on. The network may indicate what PDU of layer/sublayeris transmitted to the first UE and the second UE in advance.

The link converter of the second UE a transmittable transport block inan aspect of MAC of the second UE aspect to the RLC sublayer of thesecond UE through the link converter of the first UE. Based on theinformation, the RLC sublayer of the second UE may perform a repartitionof an RLC PDU.

Meanwhile, the ACK/NACK of an eNB for a data transmission of the firstUE that the second UE acts as a proxy for may be forwarded to the firstUE. For example, when the first UE generates an RLC PDU and transmits itto the second UE, and accordingly, the second UE transmits the data tothe eNB and receives a RLC STATUS REPORT meaning an ACK for it, thesecond UE may notify that the RLC PDU transmission of the first UE issucceeded by transmitting an RLC control PDU meaning an ACK for the RLCPDU. For this, the link converter may setup a sequence number (SN) fieldto a value (i.e., an SN value of the ACK corresponding to an SN of theRLC PDU that the first UE transmits to the second UE) that the first UEis expected to receive. As another method of forwarding the ACK/NACK ofthe eNB for the data transmission of the first UE that the second UEacts as a proxy for the RLC STATUS PDU, when the second UE receives anRLC PDU from the first UE, the method is applicable that the second UEtransmits an RLC control PDU meaning an ACK to the first UE first, andthe second UE guarantees a successful transmission of the RLC PDU. Inthis paragraph, the example of the feedback (ACK/NACK) to the RLC layeris described, but the method may also be applied to the feedback inother layer like PDCP, MAC, and so on.

Using the R field, it may be indicated whether the data includes aspecific MAC CE or at least one MAC CE. Similarly, using the R field, itmay be indicated whether the data includes a specific RLC control PDU orat least one RLC control PDU. Similarly, using the R field, it may beindicated whether the data includes a specific PDCP control PDU or atleast one PDCP control PDU. Using the R field, it may be indicatedwhether the MAC PDU includes the data (e.g., VoIP) for a real timeservice which is sensitive to latency or includes only the data(internet traffic) which is not sensitive to latency relatively, notincluding the data (e.g., VoIP) for a real time service which issensitive to latency.

In the case that the inter-UE direct link is the direct communicationlink (sidelink) based on LTE, the L and T fields may be included in theMAC header of the Sidelink MAC PDU. In this case, the L field may besetup as a MAC PDU always.

Meanwhile, it is available that the first UE separately generates a MACcontrol element (CE) and transmits it to the second UE through theinter-UE direct link. The second UE that receives it transmits it to theeNB. When constructing a MAC PDU including the MAC CE, the second UE mayindicate that the MAC CE is a MAC CE that another UE is going totransmit through a specific field of the header of the MAC PDU orintroducing a new field, or through a specific field in the MAC CE partor introducing a new field. For example, the second UE may indicate thatthe MAC PDU includes an identifier of the first UE or the MAC CE is aMAC CE of another UE, that is, a MAC CE for proxy transmission.

The case will be described that the second UE acts as a proxy for a datareception of the first UE. 1) It is available to transmit an SDUprocessed up to a specific sublayer of the second UE to the first UE andto make the first UE perform a post process. 2) As another method, it isavailable that after the second UE constructs up to a PDCP SDU, thesecond UE transmits it to the first UE. Even in this case, the functionof a data format or a link converter defined in the inter-UE direct linkdescribed above is applied. However, When the received data is a MAC SDUin the aspect of the first UE, the data is transmitted to an RLC, whenthe received data is an RLC SDU, the data is transmitted to a PDCP, andwhen the received data is a PDCP SDU, it is forwarded to a higher layer(e.g., IP layer). It may be indicated which method is to be used amongthe two methods by the network to the UE.

Reference to FIG. 16 again, a procedure (step, S1640) will be describedfor transmitting a signal received from the first UE to the second UE inFIG. 16.

In the case that the second UE that determines to perform the proxyoperation receives the data to be transmitted from the first UE to thenetwork, the second UE request an uplink transport resource for the datatransmission to the eNB.

The second UE may perform the uplink resource request for the datatransmission through a scheduling request (RS) resource which isdedicated to the first UE. For example, the second UE may transmit thescheduling request through a PUCCH configured for each UE according tothe configuration of the eNB.

Alternatively, the second UE may perform the uplink resource request forthe data transmission through a scheduling request resource which isdedicated to the second UE. For example, the second UE does not setup aseparate PUCCH for each UE, but may transmit the scheduling request ofthe first UE through the PUCCH.

Or, the second UE may also perform the uplink resource request for thedata transmission through a random access procedure. For example, thesecond UE may perform the scheduling request for being allocated withthe uplink resource from the network through the random access procedurein order to act as a proxy for the uplink transmission operation of thefirst UE. In this case, the second UE may perform a contentionresolution using a UE ID of the first UE during the random accessprocedure. The eNB may allocate a separate random access preamble groupfor the proxy operation like the scheduling request transmission and thelike described above. In this case, the second UE uses the separaterandom access preamble during the random access procedure for the proxyof the uplink transmission operation of the first UE. Through aconfiguration of a serving cell, the second UE may construct a PUCCHchannel for itself and a PUCCH channel for the first UE separately, andmay transmit by separately constructing scheduling request/HARQfeedback/CSI and the like for the second UE and scheduling request/HARQfeedback/CSI and the like for the first UE.

In order to act as a proxy for a buffer status report of the first UE,the second UE may induce the buffer status report distinguished for eachUE and transmit it.

In addition, the random access procedure may be operated in parallel bydistinguishing it for each UE.

In the case that the second UE determines to perform the proxyoperation, for example, in the case that the second UE determines totransmit the data that is going to be transmitted to the network by thefirst UE in place of the first UE, the second UE may receive thescheduling information for the data transmission of the first UE fromthe first UE, and may transmit the data that the first UE is going totransmit to the network through the uplink data channel which isdetermined based on the scheduling information. The uplink data channelmay be a physical uplink shared channel (PUSCH).

In the case that the second UE acts as a proxy for the data transmissionof the first UE, the second UE may act as a proxy for the PHY, MAC, RLCand PDCP operations that are performed when the first UE is going totransmit data to the eNB. The second UE may transmit data using arequired configuration among the PHY, MAC, RLC and PDCP of the first UE.

Alternatively, in the case that the second UE acts as a proxy for thedata transmission of the first UE, the second UE may perform the proxytransmission operation and the PHY, MAC, RLC and PDCP operationsaccording to it according to at least one configuration of PHY, MAC, RLCand PDCP that may be used when performing the proxy operation.

Meanwhile, the second UE may receive a BSR of the first UE for an uplinktransmission from the first UE. The second UE may identify the BSR ofthe first UE as an uplink buffer status of a proxy radio bearer. The BSRmay be forwarded to the eNB through a PUSCH.

The second UE may designate the proxy radio bearer as a separate logicalchannel group (LCG) according to the indication of the eNB, and mayprocess the buffer status of the first UE to be the buffer status of theLCG.

Alternatively, the second UE may construct a proxy buffer status reportMAC control element including the buffer status of the first UE. Theproxy buffer status report may be processed by being distinguished fromthe existing BSR that includes the buffer status of the second UE only.In order to indicate to which UE the BSR is related, the second UE mayinclude the a UE identifier in the BSR or may include the informationindicating that it is the proxy operation buffer status report in thebuffer status report MAC CE or the corresponding MAC header.

The eNB may allocate an uplink grant of the second UE as followsaccording to the scheduling request and the BSR received from the secondUE.

The eNB may allocate an uplink grant without distinguishing the uplinkgrant for the uplink data of the first UE and the uplink grant for theuplink data of the second UE. In this case, in the uplink grantidentified by an identifier (e.g., RNTI) of the second UE, both of theuplink grant for the uplink data of the first UE and the uplink grantfor the uplink data of the second UE are included. The second UEmonitors the RNTI of the second UE only.

Otherwise, the eNB may allocate an uplink grant by distinguishing theuplink grant for the uplink data of the first UE and the uplink grantfor the uplink data of the second UE. In this case, the uplink grantidentified by an identifier (e.g., RNTI) of the first UE isdistinguished from the uplink grant identified by an identifier of thesecond UE. The second UE monitors both of the RNTI of the first UE andthe RNTI of the second UE.

For the uplink transmission, the second UE may apply the priority asfollows.

-   -   The BSR of the first UE has lower priority than the MAC control        element (C-RNTI, BSR and PHR) and the uplink control channel        data. Alternatively, the BSR of the first UE has the same        priority as the BSR of the second UE.    -   The BSR of the first UE has higher priority than the data of the        second UE.    -   The BSR of the first UE has higher priority than the padding BSR        of the second UE.    -   The data of the first UE has a priority lower than or the same        as the data of the second UE.    -   The data of the first UE has a priority higher than or the same        as the data of the second UE.

FIG. 19 illustrates an operation method for a proxy transmission of thesecond UE.

Referring to FIG. 19, the second UE requests the resource for a datatransmission of the first UE in a network (step, S1710). The data of thefirst UE may be a user data induced from the first UE or a control datalike a response to the RRC message received from the network, and so on.

The second UE transmits the data of the first UE in place of the firstUE using the resource allocated by the network (step, S1720). Afterbeing allocated with the resource from the network in response to theresponse to the request, the second UE may transmit the data of thefirst UE using the allocated resource.

FIG. 20 is a flowchart for a method for acting as a proxy for themobility operation according to an embodiment of the present invention.

Referring to FIG. 20, a UE (e.g., the first UE) among a plurality of UEs(e.g., the first UE and the second UE) may determine to perform a proxyoperation (step, S2010). In this case, the detailed example of theprocedure of determining to perform the proxy operation is as describedabove. Hereinafter, among the procedures of determining to perform theproxy operation, particularly, the procedure of negotiating to providethe proxy service of the mobility operation with each other will bedescribed.

Here, the proxy service of the mobility operation may be intended toomit or decrease the procedure in relation to the mobility for a UE(e.g., the first UE) provided with the service. In this case, the UEprovided with the service may be in the RRC idle state. Hereinafter, forthe convenience of description, “proxy service of the mobilityoperation”, “mobility proxy service”, “acting as a proxy for theprocedure in relation to the mobility” or “mobility managementprocedure” and the like are described with being mixed. All of thoseexpression may mean that another UE performs the proxy operation,particularly, the operation in relation to the mobility.

More particularly, any one UE (e.g., the second UE) determines to act asa proxy for a procedure required for a mobility management, that is, amobility operation of other UE (e.g., the first UE). As a result, it maybe regarded that the other UE (e.g., the first UE) authorizes the one UE(the second UE) with the mobility management procedure. According to theprocedure, the one UE (the second UE) determines the mobility proxyservice for the other UE (the first UE), and the one UE (the second UE)performs the procedure according to the mobility proxy serviceprovision. Hereinafter, this may be referred to as the one UE (e.g., thesecond UE) performs the mobility proxy procedure for the other UE (thefirst UE). In this case, the UE (the first UE) that authorizes the proxyof the mobility procedure may be in an RRC idle state. Here, for theconvenience of description, it has been described that the second UEacts as a proxy for the mobility operation of the first UE, but thepresent invention is not intended to exclude the case that the first UEacts as a proxy for the mobility operation of the second UE from thescope.

When determining to provide the mobility proxy service, it may berequired that the information indicating the ID of the UE (e.g., thefirst UE) provided with the service or the paging occasion is forwardedto the UE (e.g., the second UE) that provides the service. That is, thesecond UE may act as a proxy for the paging reception of the first UEbased on the ID of the first UE received from the first UE and/or theinformation indicating the paging occasion.

One UE (e.g., the first UE or the second UE) between two UEs (e.g., thefirst UE and the second UE) may notify the information indicating thatthe mobility proxy is determined between UEs to a network. That is, theinformation indicating that any one UE is to act as a proxy for themobility procedure of another UE is provided to the network. Forexample, the UE (e.g., the second UE) that is going to act as a proxyfor the mobility procedure may notify that it determines to act as aproxy for the mobility procedure to its own serving cell. As anotherexample, the UE (e.g., the second UE) that is going to act as a proxyfor the mobility procedure may notify that it determines to act as aproxy for the mobility procedure of the first UE to its own serving CN(e.g., an MME) through a NAS message.

Later, the UE (e.g., the first UE) that authorizes the mobilityprocedure enters the power saving mode (step, S2020). In this case, thedetailed operation procedure of the UE (e.g., the first UE) that entersthe power saving mode is as described above, and only the operation inrelation to the mobility proxy procedure of the UE that enters the powersaving mode will be described below.

More particularly,

-   -   It may be regarded that the first UE authorizes other procedure        (e.g., system information monitoring procedure) that is required        for the first UE to perform in a serving cell as well as the        mobility management procedure to the second UE.    -   The first UE may not perform the measurement of serving        cell/neighboring cell that is required for performing a        reselection procedure. As a result, the first UE may omit the        performance of the reselection evaluation and the reselection in        comparison with the normal operation.    -   The first UE may perform the measurement of serving        cell/neighboring cell that is required for performing a        reselection procedure with low frequency. As a result, the first        UE may omit the performance of the reselection evaluation and        the reselection in comparison with the normal operation.    -   The first UE may omit the paging reception or may perform the        paging reception with low frequency in order to maintain an SIB        as being latest.    -   The first UE may omit the paging reception or may perform the        paging reception with low frequency in order to receive an        emergency message.

Later, the UE (the second UE) authorized with the mobility procedureacts as a proxy for the mobility operation for the UE (the first UE)that authorizes the mobility procedure (step, S2030).

More particularly, the second UE performs a measurement for its ownmobility management. Here, 1) in the case that the second UE is in theRRC idle state, the second UE performs a measurement for a cellselection/reselection. The measurement may include a measurement for aserving cell and/or a neighboring cell. 2) In the case that the secondUE may perform a measurement according to a measurement configuration inthe case that the second UE is in the RRC connected state. In this case,the measurement may include a measurement for a serving cell and/or aneighboring cell.

When the serving cell of the second UE is changed according to aprocedure like the handover, the UE may transmit new serving cellinformation to the first UE, and the new serving cell information

1) When the serving cell of the second UE is changed, the second UE maytransmit the new serving cell information to the first UE as fast aspossible (or immediately), and the detailed example that the second UEmay transmit the new serving cell information to the first UE as fast aspossible (or immediately) will be described below.

2) Even in the case that the serving cell of the second UE is changed,the second UE may not transmit the new serving cell information to thefirst UE immediately. Instead, in the case that the second UE isrequested the new serving cell information from the first UE, the secondUE may transmit the new serving cell information to the first UE, andthe detailed example that the second UE may transmit the new servingcell information to the first UE in the case that the second UE isrequested the new serving cell information from the first UE will bedescribed below.

The serving cell information that the second UE transmits to the firstUE may include the following information.

-   -   Serving cell identifier (e.g., Physical cell ID, global cell        ID),    -   Serving cell frequency,    -   System information set 1: System information essential for an        RRC connected UE among the serving cell system information, that        is, the system information essential for an RRC connection        configuration (e.g., MIB, SIB1, SIB2)    -   System information set 2: System information essential for an        RRC idle UE among the serving cell system information (e.g.,        MIB, SIB1, SIB2, SIB3, SIB4-6 (e.g., SIBs including reselection        parameters)

When the second UE forwards the system information to the first UE, oneof the following methods may be used: 1) system information 1 and systeminformation set 2 may be transmitted, or 2) only system information set1 is transmitted.

When the second UE forwards the information to the first UE, theinformation may be transmitted through an inter-UE direct communicationlink or other communication link. For example, the data may betransmitted using a communication technique that may perform theinformation transmission between UEs with low power such as an inter-UEdirect communication link using Wi-Fi, a communication link between UEsusing Bluetooth or a direct communication link between UEs using LTE.

The UE (the first UE) that authorized the mobility procedure may enterthe normal mode (step, S2040). In this case, the detailed procedure forthe UE that authorized the mobility procedure to enter the normal modeis as described above, and only the content in relation to the mobilityproxy service will be described below.

More particularly, while the first UE is in the power saving mode, inthe case that the first UE needs to enter the normal mode since thefirst UE receives a paging message for the first UE or the mobileoriginating data is generated, the first UE reconfigures itself (thefirst UE) by using the serving cell information transmitted by thesecond UE. In this case, the reconfiguration of the first UE using thereceived information may similar to the reconfiguration of the UE byreceiving the information from an eNB. For example, the first UEperforms the operation such as the operation when the UE receives itthrough MIB and SIB after receiving the information described above fromthe second UE.

In addition, the first UE may attempt the synchronization process withthe indicated serving cell based on the received serving cellinformation, and the synchronization process may include downlinksynchronization. When the UE succeeded the downlink synchronization ofthe serving cell and succeeded to camp on the serving cell, the UE maytrigger an RRC Connection setup procedure for establishing an RRCconnection in the corresponding serving cell. In this case, through theprocedure described above, uplink synchronization with respect to theserving cell is performed. In addition, it is available for the first UEto notify that the UE gets out of the power saving mode and operates inthe normal mode through the random access procedure/RRC connection setupprocedure described above to the serving cell.

When the reconfiguration and the downlink synchronization are completedbased on the information that the first UE receives from the second UE,the first UE returns to the normal mode. The first UE may notify thefact that the first UE returns to the normal operation mode to thesecond UE that has been provided the mobility proxy service. Afterreceiving the notification, the second UE may stop providing themobility proxy service, particularly, the mobility proxy service for thefirst UE.

The method for acting as a proxy for the mobility operation according tothe present invention may be combined with the procedure of acting as aproxy for the paging of the UE that authorizes the mobility proxy of theUE that is authorized with the proxy of the mobility operation. Forexample, the second UE may be determined to perform the paging operationrequired for the cellular operation of the first UE. Hereinafter, aprocedure for the UE that is authorized with the proxy of the mobilityoperation to acting as a proxy for the paging of the UE that authorizesthe mobility proxy will be described.

FIG. 21 is a flowchart of a method for acting as a proxy for the pagingaccording to an embodiment of the present invention.

Referring to FIG. 21, A UE (e.g., the second UE) authorized with themobility procedure may monitor the paging of the UE (e.g., the first UE)that authorizes the mobility procedure (step, S2110).

More particularly, the second UE may monitor the paging on the pagingoccasion of the first UE additionally in addition to its own pagingoccasion. Or, the second UE may also monitor the paging for the first UEon its own paging occasion.

Later, the UE (e.g., the second UE) authorized with the mobilityprocedure may transmit the paging of the UE that authorizes the mobilityprocedure to the UE (e.g., the first UE) that authorizes the mobilityprocedure (step, S2120).

More particularly, the second UE identifies that the UE identity of thefirst UE in addition to its own UE identity in the received pagingmessage. Or, the second UE identifies that the group ID to which thefirst UE is belonged is included in the received paging message.

In this case, when the second UE receives the paging message includingthe UE identity of the first UE, the second UE may regard thecorresponding paging message is the paging message for the first UE.

In the case that the second UE receives a paging and determines thereceived paging is a paging message for the first UE, the second UE maynotify that the paging is received to the first UE. For this, the secondUE may forward the paging message itself to the first UE or may forwardonly the information (e.g., field(s) included in the paging message)included in the paging message.

When the second UE forwards the fact that the paging is received and/orthe information included in the paging message to the first UE, thesecond UE may transmit the corresponding information through an inter-UEcommunication link. For example, through the WLAN, the Bluetooth, orother communication device or communication link of which powerconsumption is low, the information described above may be transmittedto the corresponding UE.

Later, when the first UE receives the paging information from the secondUE, the first UE may get out of the power saving mode and perform anoperation for returning to the normal mode, and the normal mode may meana normal camped normally state. In addition, when the first UE receivesthe information from the second UE, the first UE may restart an LTEmodem operation and an LTE RF operation that were stopped.

In the case that the paging message that enables the first UE to get outof the power saving mode is the paging message indicating the mobileterminating call, the first UE may attempt the RRC connection setupprocedure for an RRC connection establishment to a serving cell.

Hereinafter, a method of combining the method for acting as a proxy forthe mobility operation and the method for acting as a proxy forperforming paging according to the present invention described abovewill be described by dividing into 1. A method for the second UE totransmit new serving cell information to the first UE as fast aspossible (or immediately) when the serving cell of the second UE ischanged and 2. A method for the second UE to transmit new serving cellinformation to the first UE when the second UE is requested the newserving cell information, whereas the second UE does not forward the newserving cell information to the first UE immediately even in the casethat the serving cell of the second UE is changed.

1. A method for the second UE to transmit new serving cell informationto the first UE as fast as possible (or immediately) when the servingcell of the second UE is changed

FIG. 22 is a flowchart for a method for acting as a proxy for themobility operation according to another embodiment of the presentinvention.

Referring to FIG. 22, the first UE may register the information of thefirst UE in a CN (e.g., an MME) (step, S2210), and the second UE mayregister the information of the second UE in a CN (step, S2215). In thiscase, the primary cell of the first UE and the second UE may be “cell1”, that is, the serving cell of the first UE and the second UE may becell 1 (step, S2220).

The first UE may operate in the normal mode (step, S2225), and thedetailed example of the first UE operating in the normal mode is asdescribed above.

The first UE and the second UE may determine that the second UE acts asa proxy for the mobility procedure of the first UE (step, S2230). Inthis case, the detailed content for the determination of acting as aproxy for the mobility procedure is as described above.

Later, the first UE operates in the power saving mode (step, S2235). Inthis case, the detailed content for operating in the power saving modeis as described above.

The second UE may receive the system information of cell 2 from cell 2(step, S2240), and in some cases, the serving cell may be changed fromcell 1 to cell 2 (step, S2245).

In this case, the second UE may transmit the information of the changedserving cell, that is, the information of cell 2 to the first UE throughan inter-UE message (e.g., a message between UEs) as fast as possible(or immediately) (step, S2250).

The second UE may monitor a paging message for the first UE, and mayreceive the paging message for the first UE (step, S2255), and thedetailed content for the second UE to monitor and receive the pagingmessage for the first UE is as described above. Here, in the presentspecification, for the convenience of description, the step (S2255) thatthe second UE monitors a paging message for the first UE, and receivesthe paging message for the first UE is described after the step (S2240)that the second UE receives the system information of cell 2, the step(S2245) that cell 2 becomes the serving cell of the second UE, and thestep (S2250) that the second UE transmits the inter-UE message to thefirst UE, but the present invention is not limited thereto. That is, inthe present invention, after the step (S2255) that the second UEmonitors a paging message for the first UE, and receives the pagingmessage for the first UE is performed, the step (S2240) that the secondUE receives the system information of cell 2, the step (S2245) that cell2 becomes the serving cell of the second UE, and the step (S2250) thatthe second UE transmits the inter-UE message to the first UE may beperformed. Furthermore, 1) the step (S2255) that the second UE monitorsa paging message for the first UE, and receives the paging message forthe first UE may be separately performed from 2) the step (S2240) thatthe second UE receives the system information of cell 2, the step(S2245) that cell 2 becomes the serving cell of the second UE, and thestep (S2250) that the second UE transmits the inter-UE message to thefirst UE, that is, either one of the procedures may be performed.

In the case that the first UE receives the paging message for the firstUE while the first UE is in the power saving mode (step, S2260), or amobile originating data is generated (step, S2265) and the first UE isneeded to enter the normal mode for communicating with a network, thefirst UE may return to the normal mode (step, S2270). At this time, inthe case that the serving cell of the second UE is changed from cell 1to cell 2 and the information of cell 2 is provided to the first UE, thefirst UE attempts to camp on cell 2 immediately, and in the case thatthe serving cell of the second UE is still cell 1, the first UE may campon cell 1. In this case, the detailed example for the UE to enter thenormal mode is as described above.

Later, the first UE may notify that the first UE performs a generaloperation, that is, returns to the normal mode to the second UE throughan inter-UE message (step, S2275).

Then, in the case that the serving cell of the first UE is cell 2, thefirst UE performs an RRC connection procedure with cell 2 (step, S2280).

2. A method for the second UE not to forward the new serving cellimmediately even in the case that the serving cell of the second UE ischanged

FIG. 23 is a flowchart for a method for acting as a proxy for themobility operation according to another embodiment of the presentinvention.

Referring to FIG. 23, the first UE may register the information of thefirst UE in a CN (e.g., an MME) (step, S2310), and the second UE mayregister the information of the second UE in a CN (step, S2315). In thiscase, the primary cell of the first UE and the second UE may be “cell1”, that is, the serving cell of the first UE and the second UE may becell 1 (step, S2320).

The first UE may operate in the normal mode (step, S2325), and thedetailed example of the first UE operating in the normal mode is asdescribed above.

The first UE and the second UE may determine that the second UE acts asa proxy for the mobility procedure of the first UE (step, S2330). Inthis case, the detailed content for the determination of acting as aproxy for the mobility procedure is as described above.

Later, the first UE operates in the power saving mode (step, S2335). Inthis case, the detailed content for operating in the power saving modeis as described above.

The second UE may receive the system information of cell 2 from cell 2(step, S2340), and in some cases, the serving cell may be changed fromcell 1 to cell 2 (step, S2345).

The second UE may monitor a paging message for the first UE, and mayreceive the paging message for the first UE (step, S2350), and thedetailed content for the second UE to monitor and receive the pagingmessage for the first UE is as described above. Here, in the presentspecification, for the convenience of description, the step (S2350) thatthe second UE monitors a paging message for the first UE, and receivesthe paging message for the first UE is described after the step (S2340)that the second UE receives the system information of cell 2 and thestep (S2345) that cell 2 becomes the serving cell of the second UE, butthe present invention is not limited thereto. That is, in the presentinvention, after the step (S2350) that the second UE monitors a pagingmessage for the first UE, and receives the paging message for the firstUE is performed, the step (S2340) that the second UE receives the systeminformation of cell 2 and the step (S2345) that cell 2 becomes theserving cell of the second UE may be performed. Furthermore, 1) the step(S2350) that the second UE monitors a paging message for the first UE,and receives the paging message for the first UE may be separatelyperformed from 2) the step (S2340) that the second UE receives thesystem information of cell 2 and the step (S2345) that cell 2 becomesthe serving cell of the second UE, that is, either one of the proceduresmay be performed.

In the case that the first UE receives the paging message for the firstUE while the first UE is in the power saving mode (step, S2355), or amobile originating data is generated (step, S2360) and the first UE isneeded to enter the normal mode for communicating with a network, thefirst UE may request serving cell information to the second UE throughan inter-UE message (step, S2365). In response to the request from thefirst UE, the second UE may transmit the information of the serving cellto the first UE (step, S2370).

Later, the first UE may return to the normal mode (step, S2375). At thistime, in the case that the serving cell of the second UE is changed fromcell 1 to cell 2 and the information of cell 2 is provided to the firstUE, the first UE attempts to camp on cell 2 immediately, and in the casethat the serving cell of the second UE is still cell 1, the first UE maycamp on cell 1. In this case, the detailed example for the UE to enterthe normal mode is as described above.

Later, the first UE may notify that the first UE performs a generaloperation, that is, returns to the normal mode to the second UE throughan inter-UE message (step, S2380).

Then, in the case that the serving cell of the first UE is cell 2, thefirst UE performs an RRC connection procedure with cell 2 (step, S2385).

In the embodiments of the present invention, a method for the second UEto act as a proxy for the handover operation is mainly described, buteach of the procedures of the embodiments of the present invention maybe combined with 1. A method for the second UE to act as a proxy for thepaging operation and 2. A method for the second UE to act as a proxy forthe mobility operation. That is, within each of the procedure of theembodiments of the present invention, 1. A procedure for the second UEto act as a proxy for the paging operation and 2. A procedure for thesecond UE to act as a proxy for the mobility operation may be combined,or before or after each of the procedure of the embodiments of thepresent invention, 1. A procedure for the second UE to act as a proxyfor the paging operation and 2. A procedure for the second UE to act asa proxy for the mobility operation may be combined.

The detailed content for each of the methods (1. A method for the secondUE to act as a proxy for the paging operation and 2. A method for thesecond UE to act as a proxy for the mobility operation) is as follows.

1. A Method for the Second UE to Act as a Proxy for the Paging Operation

Hereinafter, a method for acting as a proxy for the paging operationwill be described in more detail. For the convenience of description, 1)A method for acting as a proxy for the paging operation performed by thesecond UE is described first, 2) Later, a method for acting as a proxyfor the paging operation performed by the first UE is described.

1) First, a Method for Acting as a Proxy for the Paging OperationPerformed by the Second UE is Described in Detail.

A. A UE (e.g., the first UE) among a plurality of UEs (e.g., the firstUE and the second UE) may determine to perform a proxy operation.

More particularly, the first UE requests to act as a proxy for thepaging procedure. The request may be directly transmitted to the secondUE or transmitted to the second UE through an eNB or an MME. The secondUE determines whether to accept the request for acting as a proxy forthe paging procedure based on a user priority of the second UE for therequest or pro-configured information.

In order to perform the procedure of determining to act as a proxy forthe paging procedure described above more efficiently, the first UE mayinclude assistance information in the request (i.e., request for actingas a proxy for the paging procedure) described above.

The assistance information in this case may be as below.

-   -   UE device ID or user ID: The second UE that receives the request        may regard the request as a valid request in the case that the        request includes a specific device ID or a specific user ID.        That is, in the case that the second UE receives the request and        the request includes information of a specific device ID        configured to perform the paging proxy operation of the second        UE or an ID of a specific user configured to perform the paging        proxy operation by the second UE, the second UE may regard the        request as the valid request of determining to act as a proxy        for the paging procedure.    -   Amount of battery remains in the first UE: In the case that the        amount of battery remains of the second UE is a preconfigured        threshold value or more, the second UE may determine to accept        the request (i.e., the request of the paging proxy operation).        In the case that the request includes the information of the        amount of battery of the first UE, the second UE may determine        to accept the request only in the case that the amount of        battery of the first UE is a preconfigured threshold value or        more.    -   Information indicating a paging occasion of the first UE: The        second UE may receive the information indicating an UE ID of the        first UE or a paging occasion of the first UE through the        request, and may identify the paging occasion of the first UE.        The paging occasion may include information indicating one or        more radio frame numbers and one or more subframe numbers or an        index indicating the radio frame and the subframe.    -   List of a tracking area: The list of a tracking area means that        the tracking area update (TAU) procedure may not be performed in        the area (or cell) included in the list. By considering the list        of the tracking area, in the case that the tracking area of the        first UE is changed, the second UE may determine whether to        perform the TAU in place of the first UE.    -   Accessible PLMN list: The accessible PLMN list is a PLMN list        that the first UE may access. By considering the accessible PLMN        list, the second UE may determine whether to perform the TAU in        place of the first UE. In the case that the second UE is camping        on or accesses to a cell to which the first UE is unable to        access, the second UE may notify the fact that the second UE        accesses to the cell which is not accessible by the first UE,        and may stop providing of the proxy mobility service to the        first UE.    -   TAU periodic timer value: The timer value is information        required to perform a TAU procedure periodically, and the second        UE may act as a proxy for the TAU with the period indicated by        the timer value.

The following two methods may be considered through which area thepaging message for the UE provided with the proxy mobility is to betransmitted.

-   -   Method 1: When determining the UE (e.g., the second UE) that        provides the proxy mobility service and the UE (e.g., the first        UE) that is provided with the proxy mobility service, an MME        manages the information that a certain UE (e.g., the second UE)        provides the proxy mobility service to another UE (e.g., the        first UE). Based on the information, the MME may determine a        certain tracking area in which the paging message for the UE        provided with the proxy mobility service is to be transmitted.        For example, in the case that the second UE provides the proxy        mobility service to the first UE, a network may transmit (or        broadcast) the paging message to the first UE through the cell        belonged to the tracking area in which the second UE is located.    -   Method 2: A network may transit (or broadcast) the paging        message to the first UE through the cell belonged to the        tracking area in which the UE (e.g., the first UE) of the UE        (e.g., the first UE) provided with the proxy mobility service,        and in this case, the location of the UE may be identified by        the TAU procedure.

B. Later, the second UE performs a proxy for the paging operation forthe UE (e.g., the first UE) authorized to perform the paging operation.

More particularly, when the second UE determines to act as a proxy forthe paging operation required for a cellular operation of the first UE,the second UE may perform the following operation.

-   -   The second UE may monitor a paging additionally on the paging        occasion of the first UE in addition to the paging occasion of        the second UE.    -   The second UE may identify whether there is a UE identity of the        first UE n addition to the UE identity of the second UE itself        in the received paging message.    -   The second UE may identify whether the group ID in which the        first UE is belonged is included in the received paging message.    -   When the second UE receives the paging message including the UE        identity of the first UE, the second UE may regard the        corresponding paging message (i.e., the paging message including        the UE identity of the first UE) as the paging message for the        first UE.    -   The second UE may perform idle mode mobility (e.g., cell        selection) and a cell reselection procedure in place of the        first UE.    -   The second UE may possess the latest system information by        performing the system information monitoring operation in place        of the first UE. In this case, the system information may mean        the system information of the first UE.

While the second UE receives a paging for the first UE, the second UEmay act as a proxy for the UE location update procedure (e.g., TAU) forthe first UE. Hereinafter, based on the TAU procedure, the proxy of theUE location update procedure is described. In order for the second UE toperform the TAU for the first UE, the following method may be used.

-   -   Method 1: The second UE may generate a TAU request message in        place of the first UE, and may transmit it to an MME. According        to the method, it is assumed that the second UE receives the        parameter required to generate the TAU request message of the        first UE from the first UE or the network in advance, and the        second UE knows the parameter. For example, during the procedure        of negotiating the paging proxy operation between the first UE        and the second UE, the second UE receives the parameter included        in the TAU request message from the first UE. The parameter        means contents of the TRACKING AREA UPDATE REQUEST (TAU UPDATE)        message of 3GPP TS24.301. When the second UE generates the TAU        message, it includes the parameter of the UE identifier type,        and the parameter received from the first UE is used for most        parameters. However, in the case of a DRX configuration, it may        be considered to generate the TRACKING AREA UPDATE REQUEST        message of the first UE using the current DRX configuration        value of the second UE. In this case, when the network is going        to page the first UE, the paging is performed according to the        paging configuration of the second UE, and thus, it is easy to        perform the paging proxy reception for the first UE by the        second UE.    -   Method 2: The second UE may generate a TAU request message in        place of the first UE, and may transmit it to an MME, but the        TAU request message includes contents used for the second UE to        perform its own TAU REQUEST generally, and further includes the        identification information of the first UE.    -   Method 3: The first UE generates a TAU request message, and        transmits it through direct communication link to the second UE.        The second UE may receive a TAU message from the first UE, and        may transmit the received TAU message to a network. Here, the        first UE may enter the power saving mode immediately after        transmitting the TAU request to the second UE. Otherwise, the        first UE may enter the power saving mode immediately after        receiving a TAU accept message from the second UE in response to        the TAU request.

C: The second UE may forward the information of the paging of the firstUE to the first UE through an inter-UE direct communication link.

More particularly, in the case that the second UE receives a paging butthe second UE determines the received paging to be a paging message forthe first UE, the second UE may notify the fact that the paging isincoming to the first UE. For this, the second UE may forward the pagingmessage itself to the first UE, or may forward the information (e.g.,field(s) included in the paging message) included in the paging message.

Meanwhile, when the second UE receives a paging message for systeminformation modify notification, and in the case that a UE ID indicatingthe first UE is not included in a paging record of the paging message(i.e., the paging message for system information modify notification),the second UE may not transfer the paging message to the first UE. Afterthe second UE obtains the updated system information later, it isavailable for the second UE to transmit the updated system informationto the first UE.

Meanwhile, when the second UE receives a paging message indicating thatan emergency message is transmitted through the system information, thefollowing two methods may be considered.

-   -   Method 1: Without regard to whether the UE ID indicating the        first UE is not included in a paging record of the paging        message (i.e., the paging message through which an emergency        message is transmitted through the system information), the        second UE may transmit the paging message (i.e., the paging        message through which an emergency message is transmitted        through the system information) to the first UE, and        accordingly, the first UE may receive the emergency message        directly from a serving cell. Or,    -   Method 2: Without regard to whether the UE ID indicating the        first UE is not included in a paging record of the paging        message (i.e., the paging message through which an emergency        message is transmitted through the system information), after        the second UE receives the emergency message indicated by the        paging message, the second UE may transmit the emergency message        to the first UE.

When the second UE transfers the fact that the paging is incoming to thefirst UE and/or the information included in the paging message, thesecond UE may transmit the information (i.e., fact that the paging isincoming and/or the information included in the paging message) throughan inter-UE communication link. For example, through the WLAN, theBluetooth or other communication device and communication link of whichpower consumption is low, the information (i.e., fact that the paging isincoming and/or the information included in the paging message) may betransmitted to the corresponding UE (e.g., the first UE).

2) Later, a Method for Acting as a Proxy for the Paging OperationPerformed by the First UE is Described in Detail.

A. The first UE determines to perform the proxy operation. In this case,the detailed content for determining to perform the proxy operation isas described above.

B. Later, the first UE enters the power saving mode.

More particularly, while the second UE receives a paging for the firstUE, the first UE may not receive a paging. Accordingly, the first UE maysave the power consumption owing to the paging reception. That is, whilethe second UE acts as a proxy for the paging reception for the first UEin order to maximize the power consumption decrease, the first UE mayoperate in the power saving mode of which power consumption is low.

-   -   The power saving mode may mean an operation mode in which a UE        (e.g., the first UE) may not operate to monitor the paging        message transmitted from a network (serving cell).    -   The power saving mode may mean an operation mode in which a UE        (e.g., the first UE) may not perform a measurement for a cell        selection and a cell reselection although the UE is in an idle        mode.    -   The power saving mode may mean an operation mode in which a UE        may not operate to monitor the system information.    -   The power saving mode may be the power saving mode of 3GPP        standard.    -   The power saving mode may mean an operation mode in which a UE        may not operate to monitor the control channel (e.g., PDCCH,        E-PDCCH, etc.) indicating schedule information.

C. Later, the first UE may receive the paging information from a UE(e.g., the second UE) authorized to perform the paging operation. Inthis case, the paging information received by the first UE may mean thepaging information that the second UE described above forwards to thefirst UE.

D. Later, the first UE may return to the normal mode. More particularly,when the first UE receives the paging information from the second UE,the first UE gets out of the power saving mode, and may perform anoperation for returning to the normal mode. Here, the normal mode maymean a camped normally state. When the first UE receives informationfrom the second UE, the first UE may restart the UE operation and LTE RFoperation that was stopped or performed in low frequency. The first UEmay perform a cell selection in order to enter the normal mode, and maytry to camp on a suitable cell by receiving the system information froma network. In this case, the first UE may regard the serving cell of thesecond UE as a serving cell of the first UE. When the first UE entersthe normal mode, in the case that the first UE regards the serving cellof the second UE as the serving cell of the first UE, the time until thefirst UE camps on the serving cell may be decreased. For this (i.e.,when the first UE enters the normal mode, in order to regard the servingcell of the first UE as the same cell of the serving cell of the secondUE), the second UE may forward the serving cell information of thesecond UE and the system information of the serving cell (i.e., theserving cell of the second UE) to the first UE. The first UE may attemptto camp on by synchronizing with the cell indicated by the serving cellinformation received from the second UE preferentially. In this case,the first UE uses the serving cell information received from the secondUE, and accordingly, the first UE may camp on the corresponding cellquickly.

As a subsequent procedure, in the case that the corresponding pagingmessage is a paging message indicating a mobile terminating call afterthe first UE camps on the serving cell, the first UE may attempt an RRCconnection setup procedure for an RRC connection establishment in theserving cell.

2. A Method for the Second UT to Act as a Proxy for the Handover

Hereinafter, a method for acting as a proxy for a handover procedurewill be described in detail. For the convenience of description, 1) Amethod for acting as a proxy for a handover operation in the aspect ofthe first UE, 2) A method for acting as a proxy for a handover operationin the aspect of the second UE, and 3) A method for acting as a proxyfor a handover operation in the aspect of a source cell will bedescribed. Hereinafter, for the convenience of description, in themobility proxy operation procedure, a handover proxy operation proceduremay be included, or the mobility proxy operation procedure may be usedas the same concept of the handover proxy operation procedure.

1) A Method for Acting as a Proxy for a Handover Operation in the Aspectof the First UE

A. The first UE determines to perform the proxy operation with thesecond UE

More particularly, a UE among two or more UEs performs a procedure ofagreeing to provide a proxy mobility service to another UE. The first UErequest to perform the proxy mobility procedure to the second UE. Therequest to perform the proxy mobility procedure may be directlytransmitted to the second UE or may be transmitted via an eNB or an MME.The second UE may determine whether to accept the request based on auser preference or preconfigured information.

In the case that the first UE and the second UE determine to perform theproxy operation through signaling, a UE (i.e., the first UE or thesecond UE) among the UEs (i.e., the first UE and the second UE) inrelation to the proxy operation may notify the information that theperformance of the proxy operation is determined to a network. In thiscase, the information that the performance of the proxy operation isdetermined may be information indicating that a certain UE is going toact as a proxy for the mobility procedure of another UE. For example, aUE (e.g., the second UE) that is going to act as a proxy for themobility procedure may notify that the UE is going to act as a proxy forthe mobility procedure of the second UE to a serving cell of the secondUE. As another example, a UE (e.g., the second UE) that is going to actas a proxy for the mobility procedure may notify that the UE is going toact as a proxy for the mobility procedure of the first UE to a servingCN (e.g., an MME) of the second UE through a NAS message.

B. Later, the first UE may enter the power saving mode.

Particularly, a UE (e.g., the first UE) that is going to be providedwith the mobility proxy service from the UE (e.g., the second UE)authorized with the mobility procedure may operate in the power savingmode. The UE (e.g., the first UE) that authorizes the mobility proceduremay omit or perform with low frequency the operations that the UE shouldperform in the normal RRC-connected mode (here, the detailed contentsfor the operation that should be performed in the normal RRC-connectedmode is as described above) during the power saving mode. For example,

-   -   The UE may not perform a measurement of a serving        cell/neighboring cell which is required for the mobility        support.    -   The UE may perform a measurement of a serving cell/neighboring        cell which is required for the mobility support with lower        frequency than that of the second UE.    -   The UE may not perform a control channel monitoring required for        the mobility support.    -   The UE may perform a control channel monitoring required for the        mobility support with lower frequency than that of the second        UE.    -   The UE may not perform a control channel monitoring required for        a downlink scheduling.    -   The UE may omit a paging reception for maintaining system        information (e.g., SIB) as the latest state in a connected mode.    -   The UE may omit a paging reception for receiving an urgent        message in a connected mode.

C. When the first UE transmits UE generated data or identify UEterminating data, the first UE may return to the normal mode.

More particularly, when a mobile originating data is occurred in thefirst UE and the first UE is going to transmit the data or the first UEidentifies that there is a mobile terminating data that the first UEshould receive, the first UE may be switched from the power saving modeto the normal mode with respect to the RRC connection.

In this case, the first UE may request the information of the UEconfiguration or the serving cell that the first UE is going to use tothe second UE that provides a mobility proxy service to the first UEitself. That is, when the first UE transmits the UE generated data oridentifies the UE terminating data, the step for the first UE to returnto the normal mode may further include a step of requesting theinformation of the UE configuration or the serving cell that the firstUE is going to use to the second UE that provides a mobility proxyservice to the first UE itself.

Here, the second UE that receives the request may transmit theinformation of the serving cell or the UE configuration information thatthe first UE is going to use to the first UE. The information of theserving cell may include a serving cell identifier (i.e., informationfor identifying the serving cell), and in addition, the systeminformation of the serving cell may be also included in the informationof the serving cell. That is, in the case that the first UE transmitsthe UE generated data or identifies the UE terminating data the step forthe first UE to return to the normal mode may further include a step forthe first UE to receive the serving cell information and the UEconfiguration information that the first UE is going to use from thesecond UE.

The above described information (i.e., the serving cell informationand/or the UE configuration information) may be transmitted via thedirect communication link between UEs or other communication node. Forexample, the information (i.e., the serving cell information and/or theUE configuration information) may be transmitted by using thecommunication technique that may perform the inter-UE informationtransmission with low power such as the inter-UE direct communicationlink using the Wi-Fi, the inter-UE communication link using theBluetooth or the inter-UE direct communication link using LTE, and soon.

Later, the first UE may store the RRC configuration based on theinformation received from the second UE, and may regard the serving cellas the primary cell of the first UE based on the information of theserving cell received from the second UE.

The first UE may try to synchronize to the serving cell by using thestored RRC configuration.

More particularly, the first UE that receives the information mayreconfigure the first UE itself by using the received UE information.The reconfiguration of the first UE by using the received informationmay be seen as substantially the same as the first UE reconfigure byreceiving the received information from an eNB. That is, the process forthe first UE to perform the synchronization process with the servingcell configured to the first UE based on the information received fromthe second UE may be the same as the process for the first UE to performthe synchronization process by receiving the information from theserving cell.

The first UE may try to perform the synchronization process with respectto the serving cell indicated by the second UE based on the receivedserving cell information. The synchronization process may includedownlink synchronization and/or uplink synchronization. The uplinksynchronization may include a random access procedure, and in this case,the random access procedure may be tried for the received serving cell.Through the random access procedure, it is possible for the first UE tonotify that the UE gets out of the power saving mode and operates in thenormal mode to the serving cell.

In the case that the first UE completes the reestablishment and thesynchronization process based on the information received from thesecond UE, the first UE may return to the normal operation mode. In thiscase, the first UE may notify the fact that the first UE returns to thenormal operation mode to another UE (e.g., the second UE) that has beenproviding the mobility proxy service to the first UE.

When the UE (e.g., the second UE) that has been performing the mobilityproxy operation receives a notification of returning to the normaloperation mode from the mobility proxy target UE (e.g., the first UE),the second UE may notify that the mobility proxy target UE (e.g., thefirst UE) returns to the normal operation mode to the serving cell.

Meanwhile, the first UE may determine on whether to switch to the normaloperation mode for each bearer and/or application. For example, thefirst UE may perform the operation described above (i.e., the operationof returning to the normal mode) only when the mobile generated data isgenerated with respect to a specific bearer and/or application and thefirst UE is going to transmit data, and may operate only in the powersaving mode with respect to other bearer and/or application. Forexample, when starting a voice/video service, the first UE may beswitched the normal mode, and the first UE may operate in the powersaving mode with respect to a messaging service.

2) A Method for Acting as a Proxy for a Handover Operation in the Aspectof the First UE

A. The second UE determines to perform a proxy operation with the firstUE. In this case, the method of determining the proxy operation of thesecond UE with the first UE is as described above.

B. Later, the second UE may perform a procedure of acting as a proxy themobility of the first UE in order to act as a proxy for the operationfor the handover of the first UE.

More particularly, the second UE that plans to provide the mobilityproxy service to the first UE performs a normal operation performed inthe RRC connected mode, and performs the mobility proxy service for thefirst UE additionally. The procedure performed by the second UE mayinclude the following operation.

-   -   When transmitting a measurement report message including the        measurement result of a serving cell and/or a neighboring cell        to a serving cell, the second UE may notify that the second UE        is currently support the mobility procedure of another UE (e.g.,        the first UE).    -   Periodically or when there is a request from an eNB, the second        UE may report information on whether the second UE provides the        mobility proxy service to another UE (e.g., the first UE)        currently to a serving cell.

When the second UE notifies the information to a network (e.g., aserving cell), the second UE may transmit an ID (C-RNTI or S-TMSI) ofthe UE (e.g., the first UE) provided with the mobility proxy servicefrom the second UE to the network.

C. Later, when the second UE receives a handover command from theexisting serving cell (here, the existing serving cell may mean a sourcecell.), the second UE may perform handover to a new cell (e.g., a targetcell).

More particularly, the existing serving cell (here, the existing servingcell mean the source cell that the second UE establishes an RRCconnection originally) may transfer a handover command to the second UE.

The handover command (e.g., the handover command received by the secondUE from the source cell) includes the information enables the second UEto identify a target cell that the second UE is going to move byperforming the handover. In addition, the handover command may furtherinclude the UE configuration that the second UE is going to use in thetarget cell and the UE configuration that the target cell that thesecond UE performs the mobility proxy operation is going to use, thatis, the UE configuration that the first UE is going to use in the targetcell. In summary, the handover command may include a configuration(e.g., an RRC configuration for the first UE and/or the second UE) inrelation to the handover for the first UE and/or the second UE.

In summary, the handover message, that is, a single RRC message mayinclude an RRC message container for handover of the first UE as well asthe information element indicating the configuration for the second UE.Or, the single RRC message may include the information element (IE) ofboth of the handover of the first UE and the handover the second UE.

When the second UE receives the handover command, the second UE mayperform handover to a target cell indicated through the handovercommand. The handover command received by the second UE may include theUE configuration that another UE (e.g., the first UE) is going to use inthe target cell, and in such a case, the second UE may store the UEconfiguration for the first UE. That is, when the second UE performshandover to the target cell, the handover command received by the secondUE may include the UE configuration for the first UE to which the secondUE provides the mobility proxy service in addition to the UEconfiguration for the second UE. Accordingly, the second UE may storethe UE configuration for the first UE.

a) In the case that a problem occurs in a handover preparation processbetween eNBs during the handover procedures, or in the case that thesecond UE performs an Connection Re-establishment owing to a handoverfailure, and the like or the second UE enters an RRC idle mode, thesecond UE may notify that the proxy operation and/or the mobility proxyoperation is stopped to the first UE. When the second UE notifies thatthe proxy operation and/or the mobility proxy operation are stopped tothe first UE, the first UE may perform either one of the followingoptions.

-   -   First option: When the first UE knows that the proxy operation        and/or the mobility proxy operation are stopped, the first UE is        switched from the power saving mode to the normal mode, and a        MAC layer of the first UE may perform an uplink transmission to        a source cell through a random access procedure, a scheduling        request procedure, a Buffer Status report procedure, and so on.    -   Second option: When the first UE knows that the proxy operation        and/or the mobility proxy operation are stopped, the first UE is        switched from the power saving mode to the normal mode, and an        RRC layer of the first UE may perform an RRC Connection        Re-establishment procedure. In this case, the first UE may        perform a cell selection to a source cell or a target cell.    -   Third option: When the first UE knows that the proxy operation        and/or the mobility proxy operation are stopped, the first UE is        switched from the power saving mode to the normal mode, and an        RRC layer of the first UE notifies the switch to the normal mode        (i.e., the information that the first UE enters the normal mode)        to a source cell by transmitting an uplink RRC message.    -   Fourth option: When the first UE knows that the proxy operation        and/or the mobility proxy operation are stopped, the first UE is        switched from the power saving mode to the normal mode, and a        NAS layer of the first UE notifies the switch to the normal mode        (i.e., the information that the first UE enters the normal mode)        to an MME by transmitting an uplink NAS message, and the MME        notifies the fact (i.e., the information that the first UE        enters the normal mode) to a source cell.    -   Fifth option: When the first UE knows that the proxy operation        and/or the mobility proxy operation are stopped, the first UE is        switched from the power saving mode to the normal mode, and the        first UE enters an RRC_IDLE mode. Later, a NAS layer of the        first UE notifies the switch to the normal mode (i.e., the        information that the first UE enters the normal mode) to an MME        by transmitting an uplink NAS message.

In addition, when the proxy operation and/or the mobility proxyoperation are stopped, the first UE or the second UE may notify that thefirst UE is switched to the normal mode to an MME, and the MME maynotifies the fact (i.e., the information that the first UE enters thenormal mode) to a source cell again. As another method, the first UE orthe second UE may notify that the first UE is switched to the normalmode to a source cell directly, or to a target cell. In this case, whenthe first UE notifies the fact that the first UE is switched to thenormal mode, the target cell may notify the fact that the first UE isswitched to the normal mode to the source cell through a notification.

Furthermore, when the proxy operation and/or the mobility proxyoperation are stopped, the source cell may notify that the first UE isswitched to the normal mode to an MME.

b) Meanwhile, since a target cell does not support the proxy operationand/or the proxy mobility, the target cell may accept the handover ofthe second UE, but may not accept and/or configure the proxy operationand/or the proxy mobility. In such a case, one of the options below maybe applied to the first UE, the second UE, a source cell and a targetcell.

-   -   First option: A target cell may divide a handover command for        the first UE and a handover for the second UE, and may transfer        it to a source cell. That is, the source cell may transmit        separate handover commands to the first UE and the second UE,        respectively. In this case, the handover commend for the first        UE may also be transmitted to the first UE through the second        UE.

When the first UE a separate handover command through the source cell orthe second UE, the first UE is switched to the normal mode, and stopsthe proxy operation and/or the proxy mobility. And the first UE maytransmit an uplink message like a handover (HO) complete and the like byperforming an operation like a random access to the target cell.

-   -   Second option: While a target cell transmits a handover command        for the second UE, the target cell may notify that a separate        handover is available for the first UE to a source cell. The        source cell notifies the fact (i.e., a separate handover is        available for the first UE) to the first UE through the second        UE, and accordingly, the first UE may be switched to the normal        mode, and may stop the proxy operation and/or the proxy        mobility. Later, the first UE may transmit an uplink message        like a handover complete by performing a random access and the        like to the target cell.    -   Third option: While a target cell transmits a handover command        for the second UE, the target cell may notify that a separate        handover is available for the first UE to a source cell. In this        case, the source cell notifies the fact that a separate handover        is available for the first UE to the first UE through the second        UE, and accordingly, the first UE may be switched to the normal        mode, and may stop the proxy operation and/or the proxy        mobility. Later, the first UE may perform an RRC Connection        Re-establishment to the target cell or may perform an RRC        Connection Establishment.    -   Fourth option: While a target cell transmits a handover command        for the second UE, the target cell may notify that a separate        handover is available for the first UE to a source cell. In this        case, the source cell notifies the fact that a separate handover        is available for the first UE to the first UE through the second        UE, and accordingly, the first UE may be switched to the normal        mode, and may stop the proxy operation and/or the proxy        mobility. And, the first UE may transmit a measurement report to        the source cell. The measurement report may include the        measurement result (e.g., RSRP and/or RSRQ) of the first UE with        respect to the source cell and the target cell, and the source        cell may determine the handover of the first UE according to the        measurement result.

D. When there is a request of the first UE, the second UE may transmitthe information of the new serving cell determined by the handover tothe first UE.

More particularly, the handover command that the second UE transmits tothe first UE may be transferred through an RRC message included in anRRC container or may be transferred by the information element itself.Here, in the case that the RRC message is included in the RRC container,the second UE may reconstruct the RRC message.

3) A Method for Acting as a Proxy for a Handover Operation in the Aspectof a Source Cell

A. a source cell may identify whether the second UE is operating theproxy operation.

More particularly, when the source cell receives a measurement resultand the like from the second cell or determines to change a serving cellof the first UE and/or the second UE based on an eNB internal reference,the source cell may identify whether the second UE acts as a proxy for amobility procedure of another UE (i.e., the first UE).

B. In the case that the second UE acts as a proxy for the mobilityprocedure of the first UE, the source cell transmits the information ofthe first UE and the second UE to a target cell.

More particularly, as described above, when the source cell knows thatthe second UE is performing a proxy operation, while the source cellperforms a handover preparation procedure to a target cell, the sourcecell may perform the handover preparation procedure for a UE (e.g., thefirst UE and/or the second UE) that requires the mobility to the targetcell. In summary, the source cell may perform the preparation procedureof the handover for the first UE as well as handover for the second UE.

For example, when the source cell performs the handover preparationprocedure to the target cell, that is, in the case that the UE requiringthe mobility, that is the UE (i.e., the second UE) required to performthe handover performs the mobility procedure for another UE (e.g., thefirst UE), the source cell may transfer the information of the targetcell (i.e., the first UE) in which the mobility procedure is supportedby the second UE to the target cell as well as the information of thesecond UE. Here, the information that the source cell transfers to thetarget cell may include an AS configuration and an AS context of the UE.

In the case that the source cell does not know the AS configuration ofthe UE (i.e., the first UE) that is supported with the mobilityprocedure, the source cell may notify the fact that it is required tofetch the AS configuration for the first UE to the target cell. Thetarget cell that receives the notification may request a core network(CN) to transmit the UE capability of the UE (i.e., the first UE).

C. The source cell may receive a handover command for the first UEand/or the second UE from the target cell.

More particularly, when the target cell completes the handoverpreparation procedure successfully, the target cell may transfer thehandover command including the UE configuration that one or more UEs(e.g., the first UE and/or the second UE) are going to use in the targetcell to the source cell. That is, the source cell may receive thehandover command including the UE configuration that the first UE and/orthe second UE are going to use in the target cell from the target cell.In other words, according to the present invention in which one UE(e.g., the second UE) performs the proxy mobility for another UE (e.g.,the first UE), the target cell may transfer the UE configuration thatthe first UE and/or the second UE are going to use in the target cell tothe source cell.

In order to support the procedure above described, in the case that thetarget cell supports the proxy operation and/or the proxy mobility, thetarget cell may notify whether itself (i.e., the target cell) supportsthe proxy operation and/or the proxy mobility to neighboring cellsincluding the source cell through X2 interface. Or, an MME may notifywhether to support the proxy operation and/or the proxy mobility tolower cells (i.e., a cell subjected to the MME).

Meanwhile, the handover preparation procedure may be progressed only forthe second UE (e.g., the handover preparation procedure may not beprogressed for the first UE). For example, in the case that the targetcell does not support the proxy mobility service, the target cell doesnot support the power saving mode or the target cell is in short ofnetwork resource and/or radio resource for supporting the first cell(i.e., for providing a communication to the first UE), the target cellmay accept the handover of the second UE but fails to accept thehandover of the first UE.

Accordingly, during the handover preparation procedure, the target cellmay notify the information that only the handover of the second UE isrejected selectively.

In the case that the target cell selectively accepts the handover for apart of UEs (e.g., only the second UE) and the handover of the first UEis rejected, according to the determination of the source cell, only thesecond UE may perform handover to the target cell. In this case, thesource cell or the second UE may notify that the proxy operation and/orthe proxy mobility are stopped to the first UE.

Meanwhile, the target cell may not support the proxy operation and/orthe proxy mobility originally as described above. In the case that thetarget cell does not notify that the proxy operation and/or the proxymobility are not supported, the source cell may perform the handoverpreparation procedure separately for the first UE and the second UE. Inthis case, the handover is attempted to the target cell in which theproxy operation and/or the proxy mobility are not supported, the sourcecell or the second cell may notify that the proxy operation and/or theproxy mobility are stopped.

FIG. 24 is a block diagram illustrating a UE in which the embodiments ofthe present invention are implemented.

Referring to FIG. 24, a UE 1100 includes a processor 1110, a memory 1120and a radio frequency (RF) unit 1140. The processor 1110 implements theproposed functions, processes and/or methods.

The RF unit 1140 is connected with the processor 1110, and transmits andreceives radio signals.

The processor may include an application-specific integrated circuit(ASIC), a separate chipset, a logic circuit, and/or a data processingunit. The memory may include a read-only memory (ROM), a random accessmemory (RAM), a flash memory, a memory card, storage medium, and/orother equivalent storage devices. The RF unit may include a base-bandcircuit for processing a radio signal. When the embodiment of thepresent invention is implemented in software, the aforementioned methodscan be implemented with a module (i.e., process, function, etc.) forperforming the aforementioned functions. The module may be stored in thememory and may be performed by the processor. The memory may be locatedinside or outside the processor, and may be coupled to the processor byusing various well-known means.

What is claimed is:
 1. A method for operating a power saving modeperformed by a first user equipment (UE) in a wireless communicationsystem, the method comprising: determining whether a second UE acts aproxy for a procedure in relation to mobility for the first UE; andentering a power saving mode based on the determination, wherein theprocedure in relation to mobility of the first UE is not performed orperformed with low frequency in the power saving mode.
 2. The method ofclaim 1, wherein a user of the first UE and a user of the second UE areidentical, and wherein an amount of battery of the first UE is smallerthan an amount of battery of the second UE.
 3. The method of claim 1,further comprising transmitting information of the determination to anetwork.
 4. The method of claim 1, wherein, in the power saving mode, ameasurement of a serving cell and a neighboring cell required forperforming the procedure in relation to mobility is not performed, ameasurement of a serving cell and a neighboring cell required forperforming the procedure in relation to mobility is performed with lowfrequency in comparison with the second UE, a paging reception isomitted, or a paging reception is performed with low frequency.
 5. Themethod of claim 1, further comprising receiving information of a servingcell through the second UE, in the power saving mode.
 6. The method ofclaim 5, wherein the information of the serving cell includes at leastone of a serving cell identity, a serving cell frequency, systeminformation set 1, or system information set
 2. 7. The method of claim5, further comprising: receiving a paging message for the first UEthrough the second UE; and returning to a normal mode based on theinformation of the serving cell.
 8. The method of claim 7, furthercomprising transmitting the information indicating returning to thenormal mode to the second UE after returning to the normal mode.
 9. Themethod of claim 5, further comprising returning to a normal mode basedon the information of the serving cell when a mobile originating data isgenerated.
 10. The method of claim 5, further comprising: receiving apaging message for the first UE through the second UE; requesting theinformation of the serving cell to the second UE; and returning to anormal mode based on the information of the serving cell, whereinreceiving the information of the serving cell through the second UE isperformed after requesting the information of the serving cell.
 11. Themethod of claim 5, further comprising: requesting the information of theserving cell to the second UE when a mobile originating data isgenerated; and returning to a normal mode based on the information ofthe serving cell, wherein receiving the information of the serving cellthrough the second UE is performed after requesting the information ofthe serving cell to the second UE.
 12. The method of claim 1, whereinthe first UE is in a Radio Resource Control (RRC) idle state.
 13. A userequipment (UE), the UE comprising: a radio frequency (RF) unitconfigured to transmit and receive a radio signal; and a processorconfigured to operate with being connected with the RF unit, wherein theprocessor is configured to perform: determining whether another UE actsa proxy for a procedure in relation to mobility for the UE; and enteringa power saving mode based on the determination, wherein the procedure inrelation to mobility of the UE is not performed or performed with lowfrequency in the power saving mode.